d/freebsd-nq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

crunchgen: remove -dc from linker invocation

Browse Source 
In GNU ld and ld.lld, -dc is used with -r to allocate space to COMMON
symbols.  It is presumably to work around legacy code which cannot
handle COMMON symbols in relocatable output.  ld.lld may remove -dc or
make it a no-op for the 15.0.0 release.

As of 7420b323a014 crunch/crunchide does not require -dc, as the symbol
hiding technique no longer relied on making symbols local.

In addition -fno-common is now the default in Clang and GCC, so -dc
serves no purpose as the compiler does not generate COMMON symbols
anyway.

See https://maskray.me/blog/2022-02-06-all-about-common-symbols for more
detail on common symbols.

Reviewed by:	emaste
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D34215
This commit is contained in:
Fangrui Song 2022-02-08 19:59:53 -05:00 committed by Ed Maste
parent d73d40c17f
commit ec81497cc7
2 changed files with 3 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
usr.sbin/crunch/crunchgen/crunchgen.c
View File

@ -1123,7 +1123,7 @@ prog_makefile_rules(FILE *outmk, prog_t *p)
fprintf(outmk, " $(%s_LIBS)", p->ident);
fprintf(outmk, "\n");
fprintf(outmk, "\t$(CC) -nostdlib -Wl,-dc -r -o %s.lo %s_stub.o $(%s_OBJPATHS)",
fprintf(outmk, "\t$(CC) -nostdlib -r -o %s.lo %s_stub.o $(%s_OBJPATHS)",
p->name, p->name, p->ident);
if (p->libs)
fprintf(outmk, " $(%s_LIBS)", p->ident);

6
usr.sbin/crunch/crunchide/crunchide.c
View File

@ -28,9 +28,7 @@
/*
* crunchide.c - tiptoes through a symbol table, hiding all defined
* global symbols. Allows the user to supply a "keep list" of symbols
* that are not to be hidden. This program relies on the use of the
* linker's -dc flag to actually put global bss data into the file's
* bss segment (rather than leaving it as undefined "common" data).
* that are not to be hidden.
*
* The point of all this is to allow multiple programs to be linked
* together without getting multiple-defined errors.
@ -40,7 +38,7 @@
* int foo_main(int argc, char **argv){ return main(argc, argv); }
* like so:
* cc -c foo.c foostub.c
* ld -dc -r foo.o foostub.o -o foo.combined.o
* ld -r foo.o foostub.o -o foo.combined.o
* crunchide -k _foo_main foo.combined.o
* at this point, foo.combined.o can be linked with another program
* and invoked with "foo_main(argc, argv)". foo's main() and any