https://llvm.org/bugs/show_bug.cgi?id=25837
Bug ID: 25837
Summary: Absent alignment field in .comm differs from GAS
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: MC
Assignee: unassignedb...@nondot.org
Reporter: dan433...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
The interpretation of an absent alignment field in .comm (and .lcomm)
directives in llvm-mc differs from GAS:
$ cat comm.s
.comm foo,256
$ as comm.s -o comm.o
$ readelf -sW comm.o |grep foo
4: 0000000000000010 256 OBJECT GLOBAL DEFAULT COM foo
$ llvm-mc -filetype=obj -o comm.o comm.s
$ readelf -sW comm.o |grep foo
1: 0000000000000001 256 OBJECT GLOBAL DEFAULT COM foo
Note that for COMMON symbols, the Value field holds the alignment, so it's 16
for GAS here and 1 for llvm-mc.
The GAS behavior is documented on this page:
https://sourceware.org/binutils/docs/as/Comm.html#Comm
"If no alignment is specified, as will set the alignment to the largest power
of two less than or equal to the size of the symbol, up to a maximum of 16 on
ELF, or the default section alignment of 4 on PE."
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