Not getting fs_base from gdb when running rr replay on an Intel J4105 processor

[Frederick888]

I was trying to set up remote rr replay when I noticed delve wasn't
giving my DAP client thread IDs in 'stopped by breakpoint' messages
(hence clients were not querying frames, scopes or variables either).

After spending some time on delve's code, I realised that delve wasn't
able to get address of fs_base register at [1], and therefore not able
to correctly read process memory at [2], causing all the weird issues I
was experiencing. GDB responses here were shorter than expected and fs_base's
reg.value referenced the empty part of regs.buf at its end.

However interestingly, if I run rr replay directly, I was actually
able to see fs_base address in GDB. To help demonstrate the issue, I
added some debug logs and a sample hello_world project in my fork [3].

git clone https://github.com/Frederick888/delve.git && cd delve
git checkout 1.8.2-debug
go build github.com/go-delve/delve/cmd/dlv
cd hello_world
go test -c -o ./main.test -gcflags=all='-N -l' ./
rr record -o ./trace ./main.test -test.v
cd ..

Now in delve (irrelevant output omitted):

$ ./dlv replay --log --log-output=gdbwire ./hello_world/trace
(dlv) b lib_test.go:29
(dlv) c
2022-03-19T07:00:56+11:00 debug layer=gdbconn Expecting fs_base at 544
2022-03-19T07:00:56+11:00 debug layer=gdbconn <- $Hgp2061fc.2061fc#71
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> Response size: 4
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [24 4f 4b 23]
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> $OK#9a
2022-03-19T07:00:56+11:00 debug layer=gdbconn <- $g#67
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> Response size: 1090
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [24 61 30 32 31 30 39 30 30 63 30 30 30 30 30 30 30 32 30 37 61 35 34 30 30 30 30 30 30 30 30 30 30 36 30 30 30 30 31 30 30 63 30 30 30 30 30 30 30 32 30 61 35 30 34 30 30 63 30 30 30 30 30 30 30 33 37 66 65 36 38 31 39 30 30 30 30 30 30 30 30 62 30 32 32 30 39 30 30 63 30 30 30 30 30 30 30 38 38 31 65 30 36 30 30 63 30 30 30 30 30 30 30 66 30 31 64 30 36 30 30 63 30 30 30 30 30 30 30 63 30 31 61 30 36 30 30 63 30 30 30 30 30 30 30 30 31 30 30 30 30 30 30 30 30 30 30 30 30 30 30 39 38 38 31 30 31 30 30 63 30 30 30 30 30 30 30 34 36 30 32 30 30 30 30 30 30 30 30 30 30 30 30 37 30 31 65 30 36 30 30 63 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 34 30 32 33 30 39 30 30 63 30 30 30 30 30 30 30 64 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 35 37 37 61 35 34 30 30 30 30 30 30 30 30 30 30 30 36 30 32 30 30 30 30 33 33 30 30 30 30 30 30 32 62 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 37 66 30 33 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 64 30 32 30 36 31 30 30 30 30 30 30 30 30 30 30 30 30 33 30 36 32 30 30 30 30 30 30 30 30 30 30 30 30 30 30 66 66 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 64 30 36 37 30 33 30 30 63 30 30 30 30 30 30 30 64 39 64 39 34 65 30 30 30 30 30 30 30 30 30 30 61 30 32 31 30 39 30 30 63 30 30 30 30 30 30 30 32 30 61 35 30 34 30 30 63 30 30 30 30 30 30 30 32 30 61 35 30 34 30 30 63 30 30 30 30 30 30 30 61 30 32 31 30 39 30 30 63 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 38 31 61 36 34 36 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 61 30 31 66 30 30 30 30 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 23]
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> $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#e3
2022-03-19T07:00:56+11:00 debug layer=gdbconn Expected data size: 560, Parsed data size: 544
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [a0 21 09 00 c0 00 00 00 20 7a 54 00 00 00 00 00 60 00 01 00 c0 00 00 00 20 a5 04 00 c0 00 00 00 37 fe 68 19 00 00 00 00 b0 22 09 00 c0 00 00 00 88 1e 06 00 c0 00 00 00 f0 1d 06 00 c0 00 00 00 c0 1a 06 00 c0 00 00 00 01 00 00 00 00 00 00 00 98 81 01 00 c0 00 00 00 46 02 00 00 00 00 00 00 70 1e 06 00 c0 00 00 00 00 00 00 00 00 00 00 00 40 23 09 00 c0 00 00 00 d0 00 00 00 00 00 00 00 57 7a 54 00 00 00 00 00 06 02 00 00 33 00 00 00 2b 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 7f 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 d0 20 61 00 00 00 00 00 00 30 62 00 00 00 00 00 00 00 ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 d0 67 03 00 c0 00 00 00 d9 d9 4e 00 00 00 00 00 a0 21 09 00 c0 00 00 00 20 a5 04 00 c0 00 00 00 20 a5 04 00 c0 00 00 00 a0 21 09 00 c0 00 00 00 00 00 00 00 00 00 00 00 81 a6 46 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 a0 1f 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00]
2022-03-19T07:00:56+11:00 debug layer=gdbconn Got fs_base=[00 00 00 00 00 00 00 00]
2022-03-19T07:00:56+11:00 debug layer=gdbconn Expecting fs_base at 544
2022-03-19T07:00:56+11:00 debug layer=gdbconn <- $Hgp2061fc.2061fd#72
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> Response size: 4
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [24 4f 4b 23]
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> $OK#9a
2022-03-19T07:00:56+11:00 debug layer=gdbconn <- $g#67
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> Response size: 1090
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [24 64 61 66 66 66 66 66 66 66 66 66 66 66 66 66 66 31 34 30 30 30 30 30 30 30 30 30 30 30 30 30 30 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 37 66 30 34 30 30 63 30 30 30 30 30 30 30 31 30 37 66 30 34 30 30 63 30 30 30 30 30 30 30 30 30 37 66 30 34 30 30 63 30 30 30 30 30 30 30 39 30 38 30 30 33 30 30 63 30 30 30 30 30 30 30 65 30 32 34 30 30 30 30 63 30 30 30 30 30 30 30 30 38 30 30 30 30 30 30 30 30 30 30 30 30 30 30 34 36 30 32 30 30 30 30 30 30 30 30 30 30 30 30 65 38 37 65 30 34 30 30 63 30 30 30 30 30 30 30 30 30 38 30 30 33 30 30 63 30 30 30 30 30 30 30 65 30 32 34 30 30 30 30 63 30 30 30 30 30 30 30 38 38 30 31 30 30 30 30 30 30 30 30 30 30 30 30 35 64 62 66 34 36 30 30 30 30 30 30 30 30 30 30 34 36 30 32 30 30 30 30 33 33 30 30 30 30 30 30 32 62 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 37 66 30 33 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 31 38 36 62 63 34 32 35 39 61 37 36 62 32 62 36 39 30 30 66 31 37 61 63 31 63 38 36 30 66 66 66 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 33 33 33 36 33 61 32 61 32 65 36 36 36 63 36 31 36 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 33 34 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 39 36 34 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 39 36 34 36 39 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 62 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 62 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 37 30 33 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 37 30 36 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 66 36 37 36 37 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 37 32 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 37 37 36 31 37 36 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 66 36 37 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 66 37 30 37 35 37 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 37 33 37 30 37 38 33 64 33 30 33 30 33 62 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 61 30 31 66 30 30 30 30 32 33 30 30 30 30 30 30 30 30 30 30 30 30 30 30 23]
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> $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#09
2022-03-19T07:00:56+11:00 debug layer=gdbconn Expected data size: 560, Parsed data size: 544
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [da ff ff ff ff ff ff ff 14 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 7f 04 00 c0 00 00 00 10 7f 04 00 c0 00 00 00 00 7f 04 00 c0 00 00 00 90 80 03 00 c0 00 00 00 e0 24 00 00 c0 00 00 00 08 00 00 00 00 00 00 00 46 02 00 00 00 00 00 00 e8 7e 04 00 c0 00 00 00 00 80 03 00 c0 00 00 00 e0 24 00 00 c0 00 00 00 88 01 00 00 00 00 00 00 5d bf 46 00 00 00 00 00 46 02 00 00 33 00 00 00 2b 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 7f 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 18 6b c4 25 9a 76 b2 b6 90 0f 17 ac 1c 86 0f ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 33 36 3a 2a 2e 66 6c 61 63 3d 30 30 3b 33 36 3a 2a 2e 6d 34 61 3d 30 30 3b 33 36 3a 2a 2e 6d 69 64 3d 30 30 3b 33 36 3a 2a 2e 6d 69 64 69 3d 30 30 3b 33 36 3a 2a 2e 6d 6b 61 3d 30 30 3b 33 36 3d 30 30 3b 33 36 3a 2a 2e 6d 6b 61 3d 30 30 3b 33 36 3a 2a 2e 6d 70 33 3d 30 30 3b 33 36 3a 2a 2e 6d 70 63 3d 30 30 3b 33 36 3a 2a 2e 6f 67 67 3d 30 30 3b 33 36 3a 2a 2e 72 61 3d 30 30 3b 33 36 3a 2a 2e 77 61 76 3d 30 30 3b 33 36 3a 2a 2e 6f 67 61 3d 30 30 3b 33 36 3a 2a 2e 6f 70 75 73 3d 30 30 3b 33 36 3a 2a 2e 73 70 78 3d 30 30 3b 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 a0 1f 00 00 23 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00]
2022-03-19T07:00:56+11:00 debug layer=gdbconn Got fs_base=[00 00 00 00 00 00 00 00]
2022-03-19T07:00:56+11:00 debug layer=gdbconn Expecting fs_base at 544
2022-03-19T07:00:56+11:00 debug layer=gdbconn <- $Hgp2061fc.2061fe#73
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> Response size: 4
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [24 4f 4b 23]
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> $OK#9a
2022-03-19T07:00:56+11:00 debug layer=gdbconn <- $g#67
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> Response size: 1090
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [24 64 61 66 66 66 66 66 66 66 66 66 66 66 66 66 66 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 66 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 38 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 34 38 38 35 30 33 30 30 63 30 30 30 30 30 30 30 38 30 39 65 30 34 30 30 63 30 30 30 30 30 30 30 32 38 39 65 30 34 30 30 63 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 34 36 30 32 30 30 30 30 30 30 30 30 30 30 30 30 34 30 32 64 34 34 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 32 64 30 30 30 30 63 30 30 30 30 30 30 30 34 38 30 30 30 30 30 30 30 30 30 30 30 30 30 30 36 33 63 35 34 36 30 30 30 30 30 30 30 30 30 30 34 36 30 32 30 30 30 30 33 33 30 30 30 30 30 30 32 62 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 37 66 30 33 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 65 66 33 39 66 61 66 65 34 32 32 65 31 36 63 31 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 33 33 33 36 33 61 32 61 32 65 36 36 36 63 36 31 36 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 33 34 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 39 36 34 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 39 36 34 36 39 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 62 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 36 62 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 37 30 33 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 64 37 30 36 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 66 36 37 36 37 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 37 32 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 37 37 36 31 37 36 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 66 36 37 36 31 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 36 66 37 30 37 35 37 33 33 64 33 30 33 30 33 62 33 33 33 36 33 61 32 61 32 65 37 33 37 30 37 38 33 64 33 30 33 30 33 62 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 61 30 31 66 30 30 30 30 63 61 30 30 30 30 30 30 30 30 30 30 30 30 30 30 23]
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> $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#86
2022-03-19T07:00:56+11:00 debug layer=gdbconn Expected data size: 560, Parsed data size: 544
2022-03-19T07:00:56+11:00 debug layer=gdbconn -> [da ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 80 00 00 00 00 00 00 00 48 85 03 00 c0 00 00 00 80 9e 04 00 c0 00 00 00 28 9e 04 00 c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 46 02 00 00 00 00 00 00 40 2d 44 00 00 00 00 00 00 00 00 00 00 00 00 00 00 2d 00 00 c0 00 00 00 48 00 00 00 00 00 00 00 63 c5 46 00 00 00 00 00 46 02 00 00 33 00 00 00 2b 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 7f 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ef 39 fa fe 42 2e 16 c1 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 33 36 3a 2a 2e 66 6c 61 63 3d 30 30 3b 33 36 3a 2a 2e 6d 34 61 3d 30 30 3b 33 36 3a 2a 2e 6d 69 64 3d 30 30 3b 33 36 3a 2a 2e 6d 69 64 69 3d 30 30 3b 33 36 3a 2a 2e 6d 6b 61 3d 30 30 3b 33 36 3d 30 30 3b 33 36 3a 2a 2e 6d 6b 61 3d 30 30 3b 33 36 3a 2a 2e 6d 70 33 3d 30 30 3b 33 36 3a 2a 2e 6d 70 63 3d 30 30 3b 33 36 3a 2a 2e 6f 67 67 3d 30 30 3b 33 36 3a 2a 2e 72 61 3d 30 30 3b 33 36 3a 2a 2e 77 61 76 3d 30 30 3b 33 36 3a 2a 2e 6f 67 61 3d 30 30 3b 33 36 3a 2a 2e 6f 70 75 73 3d 30 30 3b 33 36 3a 2a 2e 73 70 78 3d 30 30 3b 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 a0 1f 00 00 ca 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00]
2022-03-19T07:00:56+11:00 debug layer=gdbconn Got fs_base=[00 00 00 00 00 00 00 00]
(dlv) regs
    Rip = 0x0000000000547a57
    Rsp = 0x000000c000061df0
    Rax = 0x000000c0000921a0
    Rbx = 0x0000000000547a20
    Rcx = 0x000000c000010060
    Rdx = 0x000000c00004a520
    Rsi = 0x000000001968fe37
    Rdi = 0x000000c0000922b0
    Rbp = 0x000000c000061e88
     R8 = 0x000000c000061ac0
     R9 = 0x0000000000000001
    R10 = 0x000000c000018198
    R11 = 0x0000000000000246
    R12 = 0x000000c000061e70
    R13 = 0x0000000000000000
    R14 = 0x000000c000092340
    R15 = 0x00000000000000d0
 Rflags = 0x0000000000000206    [PF IF IOPL=0]
     Es = 0x0000000000000000
     Cs = 0x0000000000000033
     Ss = 0x000000000000002b
     Ds = 0x0000000000000000
     Fs = 0x0000000000000000
     Gs = 0x0000000000000000
Fs_base = 0x0000000000000000
Gs_base = 0x0000000000000000

In GDB:

$ rr replay ./hello_world/trace
GNU gdb (GDB) 11.2
(rr) b lib_test.go:29
Breakpoint 1 at 0x547a57: file /home/frederick/delve/hello_world/lib_test.go, line 29.
(rr) c
Continuing.
=== RUN   TestMyHelper
=== RUN   TestMyHelper/given_0
[New Thread 2122236.2122237]
[New Thread 2122236.2122238]

Thread 1 hit Breakpoint 1, hello_world.TestMyHelper.func1 (t=0xc0000921a0) at /home/frederick/delve/hello_world/lib_test.go:29
29                              if got := MyHelper(tt.given); got != tt.want {
(rr) i reg
rax            0xc0000921a0        824634319264
rbx            0x547a20            5536288
rcx            0xc000010060        824633786464
rdx            0xc00004a520        824634025248
rsi            0x1968fe37          426311223
rdi            0xc0000922b0        824634319536
rbp            0xc000061e88        0xc000061e88
rsp            0xc000061df0        0xc000061df0
r8             0xc000061ac0        824634120896
r9             0x1                 1
r10            0xc000018198        824633819544
r11            0x246               582
r12            0xc000061e70        824634121840
r13            0x0                 0
r14            0xc000092340        824634319680
r15            0xd0                208
rip            0x547a57            0x547a57 <hello_world.TestMyHelper.func1+55>
eflags         0x206               [ PF IF ]
cs             0x33                51
ss             0x2b                43
ds             0x0                 0
es             0x0                 0
fs             0x0                 0
gs             0x0                 0
fs_base        0x63b2f0            0x63b2f0 <runtime.m0+144>
gs_base        0x0                 0x0

To add more to the craziness, I later tested this on my main machine, which's
got an i7 CPU, and I didn't have this issue at all! Responses from GDB were
larger and regs.buf got populated correctly.

I'm not terribly familiar with these things and tbh I'm not even sure if this
is a delve issue, a GDB one, or some platform-dependent weirdness. So sorry if
this is not the correct place to post this but even in that case I'd really
appreciate if someone can point me to the right direction. Thank you.

[1]

delve/pkg/proc/gdbserial/gdbserver.go

Lines 1676 to 1683 in a19931c

	if t.p.bi.GOOS == "linux" {
	if reg, hasFsBase := t.regs.regs[t.p.regnames.FsBase]; hasFsBase {
	t.regs.gaddr = 0
	t.regs.tls = binary.LittleEndian.Uint64(reg.value)
	t.regs.hasgaddr = false
	return nil
	}
	}

[2]

delve/pkg/proc/variables.go

Line 441 in a19931c

gaddr, err = readUintRaw(thread.ProcessMemory(), regs.TLS()+thread.BinInfo().GStructOffset(), int64(thread.BinInfo().Arch.PtrSize()))

[3] https://github.com/Frederick888/delve/tree/1.8.2-debug

[aarzilli]

This is a bug in rr. Do you have the ability to compile rr from source? If you do go in src/GdbServer.cc, function GdbServer::dispatch_regs_request, and change DREG_ORIG_RAX to DREG_GS_BASE. If it works I'll send a PR to rr (or you can do it, if you want -- ping me if you do).

[Frederick888]

Yup that worked! Thank you!

[Frederick888]

And I'd appreciate it if you can submit a PR to rr, since I won't be able to answer any questions if asked by rr maintainers 😅