ld: fix ELF strip by removing overlap of sections

The gosymtab and gopclntab sections were pointing to the proper
data, but that data was already owned by the rodata section.
Some ELF references explicitly prohibit multiple sections from
owning the same data, and strip behaves accordingly.

The data for these sections was moved to after rodata, and the
gosymtab and gopclntab sections now own their respective ranges.

This change makes strip happy both with and without -s being
provided at link time.  Note that it won't remove these sections
because they are still allocated, and that's by design since
they are necessary at runtime for generating proper backtraces
and similar introspection operations.

Unlike the previous behavior, -s will now maintain zero-sized
gosymtab and gopclntab sections.  This makes the implementation
slightly cleaner.

Fixes issue 1242.

NOTE: Tested on Linux amd64/386/arm only.

R=ality, rsc
CC=golang-dev
http://codereview.appspot.com/4639077

1 files changed, 7 insertions, 22 deletions

diff --git a/src/cmd/8l/asm.c b/src/cmd/8l/asm.c
index a9a720af1..e1ccfb8a3 100644
--- a/src/cmd/8l/asm.c
+++ b/src/cmd/8l/asm.c
@@ -83,9 +83,6 @@ enum {
 	ElfStrText,
 	ElfStrData,
 	ElfStrBss,
-	ElfStrGosymcounts,
-	ElfStrGosymtab,
-	ElfStrGopclntab,
 	ElfStrShstrtab,
 	ElfStrSymtab,
 	ElfStrStrtab,
@@ -531,10 +528,9 @@ doelf(void)
 	elfstr[ElfStrBss] = addstring(shstrtab, ".bss");
 	addstring(shstrtab, ".elfdata");
 	addstring(shstrtab, ".rodata");
+	addstring(shstrtab, ".gosymtab");
+	addstring(shstrtab, ".gopclntab");
 	if(!debug['s']) {
-		elfstr[ElfStrGosymcounts] = addstring(shstrtab, ".gosymcounts");
-		elfstr[ElfStrGosymtab] = addstring(shstrtab, ".gosymtab");
-		elfstr[ElfStrGopclntab] = addstring(shstrtab, ".gopclntab");
 		elfstr[ElfStrSymtab] = addstring(shstrtab, ".symtab");
 		elfstr[ElfStrStrtab] = addstring(shstrtab, ".strtab");
 		dwarfaddshstrings(shstrtab);
@@ -679,10 +675,11 @@ asmb(void)
 	seek(cout, sect->vaddr - segtext.vaddr + segtext.fileoff, 0);
 	codeblk(sect->vaddr, sect->len);
 
-	/* output read-only data in text segment */
-	sect = segtext.sect->next;
-	seek(cout, sect->vaddr - segtext.vaddr + segtext.fileoff, 0);
-	datblk(sect->vaddr, sect->len);
+	/* output read-only data in text segment (rodata, gosymtab and pclntab) */
+	for(sect = sect->next; sect != nil; sect = sect->next) {
+		seek(cout, sect->vaddr - segtext.vaddr + segtext.fileoff, 0);
+		datblk(sect->vaddr, sect->len);
+	}
 
 	if(debug['v'])
 		Bprint(&bso, "%5.2f datblk\n", cputime());
@@ -1083,18 +1080,6 @@ asmb(void)
 			elfshbits(sect);
 
 		if (!debug['s']) {
-			sh = newElfShdr(elfstr[ElfStrGosymtab]);
-			sh->type = SHT_PROGBITS;
-			sh->flags = SHF_ALLOC;
-			sh->addralign = 1;
-			shsym(sh, lookup("symtab", 0));
-
-			sh = newElfShdr(elfstr[ElfStrGopclntab]);
-			sh->type = SHT_PROGBITS;
-			sh->flags = SHF_ALLOC;
-			sh->addralign = 1;
-			shsym(sh, lookup("pclntab", 0));
-
 			sh = newElfShdr(elfstr[ElfStrSymtab]);
 			sh->type = SHT_SYMTAB;
 			sh->off = symo;