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authorMichael Brown2015-03-04 19:48:19 +0100
committerMichael Brown2015-03-05 01:59:38 +0100
commitfbc4ba4b4ed13cc86cb8fdea0bac6c3be0164ed5 (patch)
treea0c504e297806aa88e89a04e694333a7c5172757 /src/util
parent[build] Use REQUIRE_OBJECT() to drag in per-object configuration (diff)
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[build] Fix the REQUIRE_SYMBOL mechanism
At some point in the past few years, binutils became more aggressive at removing unused symbols. To function as a symbol requirement, a relocation record must now be in a section marked with @progbits and must not be in a section which gets discarded during the link (either via --gc-sections or via /DISCARD/). Update REQUIRE_SYMBOL() to generate relocation records meeting these criteria. To minimise the impact upon the final binary size, we use existing symbols (specified via the REQUIRING_SYMBOL() macro) as the relocation targets where possible. We use R_386_NONE or R_X86_64_NONE relocation types to prevent any actual unwanted relocation taking place. Where no suitable symbol exists for REQUIRING_SYMBOL() (such as in config.c), the macro PROVIDE_REQUIRING_SYMBOL() can be used to generate a one-byte-long symbol to act as the relocation target. If there are versions of binutils for which this approach fails, then the fallback will probably involve killing off REQUEST_SYMBOL(), redefining REQUIRE_SYMBOL() to use the current definition of REQUEST_SYMBOL(), and postprocessing the linked ELF file with something along the lines of "nm -u | wc -l" to check that there are no undefined symbols remaining. Signed-off-by: Michael Brown <mcb30@ipxe.org>
Diffstat (limited to 'src/util')
-rw-r--r--src/util/elf2efi.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/src/util/elf2efi.c b/src/util/elf2efi.c
index 1e7a99b7..e68fa5d1 100644
--- a/src/util/elf2efi.c
+++ b/src/util/elf2efi.c
@@ -478,6 +478,9 @@ static void process_reloc ( bfd *bfd __attribute__ (( unused )),
/* Skip absolute symbols; the symbol value won't
* change when the object is loaded.
*/
+ } else if ( ( strcmp ( howto->name, "R_386_NONE" ) == 0 ) ||
+ ( strcmp ( howto->name, "R_X86_64_NONE" ) == 0 ) ) {
+ /* Ignore dummy relocations used by REQUIRE_SYMBOL() */
} else if ( strcmp ( howto->name, "R_X86_64_64" ) == 0 ) {
/* Generate an 8-byte PE relocation */
generate_pe_reloc ( pe_reltab, offset, 8 );