https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83618
Bug ID: 83618
Summary: _rdpid_u32 doesn't work on 64-bit targets as gas
expects the 64-bit register
Product: gcc
Version: 7.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: craig.topper at gmail dot com
Target Milestone: ---
Trying to compile the _rdpid_u32 intrinsic on x86-64 causes the assembler to
print this
/tmp/ccbdTr5q.s: Assembler messages:
/tmp/ccbdTr5q.s:13: Error: operand type mismatch for `rdpid'
It appears that the assembler expects a 64-bit register in 64-bit mode.
This seems to be due to an odd quirk of Intel's documentation that says the
instruction writes a 64-bit register in 64-bit mode and a 32-bit register in
32-bit mode. But in reality its reading the TSC_AUX_MSR which is only 32-bit so
I suspect it always zeros the upper bits of the register in 64-bit mode. Which
would be the expected behavior if it had been documented as always using a
32-bit register. So I don't know why the docs made this distinction.
Not sure if this should be fixed in gcc or if gas should be taught to accept
both a 32-bit or 64-bit register.
