https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63435
Bug ID: 63435
Summary: Bad code with weak vs localalias on AIX
Product: gcc
Version: 4.9.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at dixie dot net.nz
Host: powerpc-ibm-aix7.1.0.0
Target: powerpc-ibm-aix7.1.0.0
Build: powerpc-ibm-aix7.1.0.0
Created attachment 33638
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33638&action=edit
testcase
Consider attached testcase.
The recvfrom function is generated as a weak symbol,
symtab_node::noninterposable_alias creates a localalias.
.weak recvfrom[DS]
.weak .recvfrom
.csect recvfrom[DS]
recvfrom:
.long .recvfrom, TOC[tc0], 0
.csect .text[PR]
.recvfrom:
-------
gcc-4.9.1 generates local alias to the weak symbol:
.lglobl .recvfrom.localalias.0
.lglobl recvfrom.localalias.0
.set .recvfrom.localalias.0,.recvfrom
.set recvfrom.localalias.0,recvfrom
-------
This local alias is called with local calling convention (missing nop):
bl .recvfrom.localalias.0
mr 9,3
-------
The linker discards the weak local recvfrom symbol, and chooses recvfrom from
libc.
The recvfrom in libc is remote and needs a nop instruction.
The linker correctly issues a diagnostic about this:
ld: 0711-768 WARNING: Object myrecvfrom.o, section 1, function .recvfrom:
The branch at address 0xc8 is not followed by a recognized no-op
or TOC-reload instruction. The unrecognized instruction is 0x7C691B78.
At runtime this results in corrupt TOC pointer (possibly requires larger
testcase to observe problems).
