[AArch64] When unavailable, fetch VG from ptrace.
I was doing some SVE tests on system QEMU and noticed quite a few failures related to inferior function calls. Any attempt to do an inferior function call would result in the following: Unable to set VG register.: Success. This happens because, after an inferior function call, GDB attempts to restore the regcache state and updates the SVE register in order. Since the Z registers show up before the VG register, VG is still INVALID by the time the first Z register is being updated. So when executing the following code in aarch64_sve_set_vq: if (reg_buf->get_register_status (AARCH64_SVE_VG_REGNUM) != REG_VALID) return false; By returning false, we signal something is wrong, then we get to this: /* First store vector length to the thread. This is done first to ensure the ptrace buffers read from the kernel are the correct size. */ if (!aarch64_sve_set_vq (tid, regcache)) perror_with_name (_("Unable to set VG register.")); Ideally we'd always have a valid VG before attempting to set the Z registers, but in this case the ordering of registers doesn't make that possible. I considered reordering the registers to put VG before the Z registers, like the DWARF numbering, but that would break backwards compatibility with existing implementations. Also, the Z register numbering is pinned to the V registers, and adding VG before Z would create a gap for non-SVE targets, since we wouldn't be able to undefine VG for non-SVE targets. As a compromise, it seems we can safely fetch the VG register value from ptrace. The value in the kernel is likely the updated value anyway. This patch fixed all the failures i saw in the testsuite and caused no further regressions. gdb/ChangeLog: 2020-03-19 Luis Machado <luis.machado@linaro.org> * nat/aarch64-sve-linux-ptrace.c (aarch64_sve_set_vq): If vg is not valid, fetch vg value from ptrace.
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2020-03-19 Luis Machado <luis.machado@linaro.org>
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* nat/aarch64-sve-linux-ptrace.c (aarch64_sve_set_vq): If vg is not
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valid, fetch vg value from ptrace.
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2020-03-19 Kamil Rytarowski <n54@gmx.com>
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* x86-bsd-nat.c (gdb_ptrace): New.
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@ -92,11 +92,26 @@ aarch64_sve_set_vq (int tid, uint64_t vq)
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bool
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aarch64_sve_set_vq (int tid, struct reg_buffer_common *reg_buf)
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{
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if (reg_buf->get_register_status (AARCH64_SVE_VG_REGNUM) != REG_VALID)
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return false;
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uint64_t reg_vg = 0;
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reg_buf->raw_collect (AARCH64_SVE_VG_REGNUM, ®_vg);
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/* The VG register may not be valid if we've not collected any value yet.
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This can happen, for example, if we're restoring the regcache after an
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inferior function call, and the VG register comes after the Z
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registers. */
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if (reg_buf->get_register_status (AARCH64_SVE_VG_REGNUM) != REG_VALID)
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{
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/* If vg is not available yet, fetch it from ptrace. The VG value from
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ptrace is likely the correct one. */
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uint64_t vq = aarch64_sve_get_vq (tid);
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/* If something went wrong, just bail out. */
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if (vq == 0)
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return false;
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reg_vg = sve_vg_from_vq (vq);
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}
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else
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reg_buf->raw_collect (AARCH64_SVE_VG_REGNUM, ®_vg);
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return aarch64_sve_set_vq (tid, sve_vq_from_vg (reg_vg));
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}
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