Red Hat Bugzilla – Bug 1466105
SIGSEGV if stepi at vmovdqa
Last modified: 2017-11-19 21:51:51 EST
Created attachment 1292776 [details]
45-line C program (12 SLOC, 33 comments) illustrating stepi at vmovdqa
Description of problem: If a 'vmovdqa' instruction is the target of a 'stepi' (single-step one instruction) or a 'continue' after a breakpoint, then a spurious SIGSEGV can be generated in the target program, even though free-running execution (no stepi, no continue) gets no SIGSEGV.
Version-Release number of selected component (if applicable):
How reproducible: every time
Steps to Reproduce:
1. Compile and link the attached program. The critical instruction is
(gdb) x/i main
0x4004a6 <main>: vmovdqa 0xc2(%rip),%xmm0 # 0x400570
The instruction byte stream is
(gdb) x/2xw main
0x4004a6 <main>: 0x056ff9c5 0x000000c2
2. Run under gdb, and stepi or continue after a breakpoint at the 'vmovdqa'
Program received signal SIGSEGV, Segmentation fault.
main (argc=0x1, argv=0x7fffffffdfa8) at prefix-sum-sse.c:39
39 x = _mm_add_epi8(x, _mm_srli_si128(x, 1));
(gdb) x/i $pc
=> 0x4004a6 <main>: vmovdqa 0xc2(%rip),%xmm0 # 0x400570
Expected results: no SIGSEGV, which is the behavior when not using gdb, or when no stepi and no continue-after-breakpoint in gdb.
Additional info: The alignment of the memory operand at 0x400570 is (0 mod 16) which is the natural alignment of "double quad word" ==> (2 * 4 * 2) bytes
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The problem persists with:
GNU gdb (GDB) Fedora 8.0.1-30.fc27