http://llvm.org/bugs/show_bug.cgi?id=9292
Summary: [MC assembler] .globl does not emit symbol if
unreferenced
Product: new-bugs
Version: trunk
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
It looks like MC does not emit a global symbol into the destination
object file for a .globl directive, if the object is not referenced.
This is an unwanted optimization, since e.g. module loaders can depend
on specific symbols to always be available, so they use .globl to force
the linker to emit the symbol.
This substantially differs from GNU as's behaviour. For example,
assemble the following sample file with GNU as and clang:
.globl foo
.globl bar
mov %eax,bar
Running "readelf -s" over the object file that GNU as produces gives:
Symbol table '.symtab' contains 6 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 SECTION LOCAL DEFAULT 1
2: 00000000 0 SECTION LOCAL DEFAULT 3
3: 00000000 0 SECTION LOCAL DEFAULT 4
4: 00000000 0 NOTYPE GLOBAL DEFAULT UND foo
5: 00000000 0 NOTYPE GLOBAL DEFAULT UND bar
Running "readelf -s" over the object file that GNU as produces gives:
Symbol table '.symtab' contains 5 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 SECTION LOCAL DEFAULT 1
2: 00000000 0 SECTION LOCAL DEFAULT 2
3: 00000000 0 SECTION LOCAL DEFAULT 3
4: 00000000 0 NOTYPE GLOBAL DEFAULT UND bar
MC should *not* remove the 'foo' symbol from the table here.
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