From e068c55d5e2f73e85d0d51a39d2a8921ce262d55 Mon Sep 17 00:00:00 2001 From: Joel Brobecker Date: Wed, 11 Jun 2014 14:07:27 +0200 Subject: [PATCH] x64-windows: Fix extraction of chained UNWIND_INFO On x86_64-windows, GDB is unable to unwind past some code in mswsock.dll. For instance: (gdb) bt #0 0x00000000778712fa in ntdll!ZwWaitForSingleObject () from C:\Windows\SYSTEM32\ntdll.dll #1 0x000007fefcfb0f75 in WSPStartup () from C:\Windows\system32\mswsock.dll Backtrace stopped: previous frame inner to this frame (corrupt stack?) The UNWIND_INFO record for frame #1's PC has a UNW_FLAG_CHAININFO flag, and so after having decoded this unwind record, GDB's decoder next tries to locate the next unwind record on the chain. Unfortunately, the location of that unwind info appears to be miscomputed. This is the expression used: chain_vma = cache->image_base + unwind_info + sizeof (ex_ui) + ((codes_count + 1) & ~1) * 2 + 8; The chain-info is expected to be right after the "Unwind codes array" which is itself after all the fields of ex_ui's struct. So the "+ 8" offset at the end should not be there. Because of that extra offset, we were reading no longer processing correct unwind info, leading the unwinder computing the wrong frame size, computing the wrong return address, etc. gdb/ChangeLog: * amd64-windows-tdep.c (amd64_windows_frame_decode_insns): Remove "+ 8" offset in computation of CHAIN_VMA. --- gdb/ChangeLog | 5 +++++ gdb/amd64-windows-tdep.c | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index e494a2aab3..939fd20a7a 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2014-08-01 Joel Brobecker + + * amd64-windows-tdep.c (amd64_windows_frame_decode_insns): + Remove "+ 8" offset in computation of CHAIN_VMA. + 2014-07-31 Doug Evans * inflow.c (child_terminal_inferior): Add comment. diff --git a/gdb/amd64-windows-tdep.c b/gdb/amd64-windows-tdep.c index 331ce775b8..cb1bac7861 100644 --- a/gdb/amd64-windows-tdep.c +++ b/gdb/amd64-windows-tdep.c @@ -826,7 +826,7 @@ amd64_windows_frame_decode_insns (struct frame_info *this_frame, CORE_ADDR chain_vma; chain_vma = cache->image_base + unwind_info - + sizeof (ex_ui) + ((codes_count + 1) & ~1) * 2 + 8; + + sizeof (ex_ui) + ((codes_count + 1) & ~1) * 2; if (target_read_memory (chain_vma, (gdb_byte *) &d, sizeof (d)) != 0) return; -- 2.34.1