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): gdb-7.12.1-48.fc25.x86_64 kernel-4.11.6-201.fc25.x86_64 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' 3. Actual results: 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 kernel-4.13.12-300.fc27.x86_64
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This bug appears to have been reported against 'rawhide' during the Fedora 30 development cycle. Changing version to '30.
This message is a reminder that Fedora 30 is nearing its end of life. Fedora will stop maintaining and issuing updates for Fedora 30 on 2020-05-26. It is Fedora's policy to close all bug reports from releases that are no longer maintained. At that time this bug will be closed as EOL if it remains open with a Fedora 'version' of '30'. Package Maintainer: If you wish for this bug to remain open because you plan to fix it in a currently maintained version, simply change the 'version' to a later Fedora version. Thank you for reporting this issue and we are sorry that we were not able to fix it before Fedora 30 is end of life. If you would still like to see this bug fixed and are able to reproduce it against a later version of Fedora, you are encouraged change the 'version' to a later Fedora version prior this bug is closed as described in the policy above. Although we aim to fix as many bugs as possible during every release's lifetime, sometimes those efforts are overtaken by events. Often a more recent Fedora release includes newer upstream software that fixes bugs or makes them obsolete.
Fedora 30 changed to end-of-life (EOL) status on 2020-05-26. Fedora 30 is no longer maintained, which means that it will not receive any further security or bug fix updates. As a result we are closing this bug. If you can reproduce this bug against a currently maintained version of Fedora please feel free to reopen this bug against that version. If you are unable to reopen this bug, please file a new report against the current release. If you experience problems, please add a comment to this bug. Thank you for reporting this bug and we are sorry it could not be fixed.