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2d07da271e
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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