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From: "gcc at dixie dot net.nz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/63435] New: Bad code with weak vs localalias on AIX
Date: Wed, 01 Oct 2014 23:13:00 -0000 [thread overview]
Message-ID: <bug-63435-4@http.gcc.gnu.org/bugzilla/> (raw)
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).
next reply other threads:[~2014-10-01 23:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-01 23:13 gcc at dixie dot net.nz [this message]
2014-10-01 23:17 ` [Bug c/63435] " gcc at dixie dot net.nz
2014-10-02 22:02 ` [Bug target/63435] " hubicka at ucw dot cz
2014-10-05 21:09 ` gcc at dixie dot net.nz
2014-10-06 19:01 ` hubicka at ucw dot cz
2021-07-18 21:21 ` pinskia at gcc dot gnu.org
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