Commit 49e414a7 authored by Tamar Christina's avatar Tamar Christina
Browse files

Remove lookup of sections by name instead use the index numbers as offsets

This patch comes from @awson

Playing with `-fsplit-sections` on Windows I've found a pile of ancient
(it was borrowed from Hugs interpreter code and I don't even know when
was it created), absolutely redundant and plain wrong code in RTS linker.

Technically it is a bug, but it doesn't break things when used with
current Windows binutils with no special linker scripts involved.

OTOH, it slows down runtime linker on Windows noticeably and thus can
be considered as a performance bug.

The nice side-effect for existing users is that GHCi now loads compiled
object code much faster on Windows.

More specifically, sections were being looked up by name by doing a loop
over all sections until the section with the given name is found.

The new approach uses the section index and finds the section in O(1) time
based on information gathered when we originally processed the section

Test Plan: ./validate (was run on GHC x86)

Reviewers: austin, awson, erikd, thomie, bgamari

Reviewed By: thomie, bgamari

Subscribers: awson, #ghc_windows_task_force

Differential Revision:

GHC Trac Issues: #11388
parent db371c10
......@@ -3232,62 +3232,6 @@ cstring_from_section_name (UChar* name, UChar* strtab)
/* Just compares the short names (first 8 chars) */
static COFF_section *
findPEi386SectionCalled ( ObjectCode* oc, UChar* name, UChar* strtab )
int i;
rtsBool long_name = rtsFalse;
COFF_header* hdr
= (COFF_header*)(oc->image);
COFF_section* sectab
= (COFF_section*) (
+ sizeof_COFF_header + hdr->SizeOfOptionalHeader
// String is longer than 8 bytes, swap in the proper
// (NULL-terminated) version, and make a note that this
// is a long name.
if (name[0]==0 && name[1]==0 && name[2]==0 && name[3]==0) {
UInt32 strtab_offset = * (UInt32*)(name+4);
name = ((UChar*)strtab) + strtab_offset;
long_name = rtsTrue;
for (i = 0; i < hdr->NumberOfSections; i++) {
UChar* n1;
UChar* n2;
COFF_section* section_i
= (COFF_section*)
myindex ( sizeof_COFF_section, sectab, i );
n1 = (UChar*) &(section_i->Name);
n2 = name;
// Long section names are prefixed with a slash, see
// also cstring_from_section_name
if (n1[0] == '/' && long_name) {
// Long name check
// We don't really want to make an assumption that the string
// table indexes are the same, so we'll do a proper check.
int n1_strtab_offset = strtol((char*)n1+1,NULL,10);
n1 = (UChar*) (((char*)strtab) + n1_strtab_offset);
if (0==strcmp((const char*)n1, (const char*)n2)) {
return section_i;
} else if (n1[0] != '/' && !long_name) {
// Short name check
if (n1[0]==n2[0] && n1[1]==n2[1] && n1[2]==n2[2] &&
n1[3]==n2[3] && n1[4]==n2[4] && n1[5]==n2[5] &&
n1[6]==n2[6] && n1[7]==n2[7]) {
return section_i;
} else {
// guaranteed to mismatch, because we never attempt to link
// in an executable where the section name may be truncated
return NULL;
/* See Note [mingw-w64 name decoration scheme] */
#ifndef x86_64_HOST_ARCH
static void
......@@ -3986,13 +3930,7 @@ ocResolve_PEi386 ( ObjectCode* oc )
if (sym->StorageClass == MYIMAGE_SYM_CLASS_STATIC) {
COFF_section* section_sym
= findPEi386SectionCalled ( oc, sym->Name, strtab );
if (!section_sym) {
errorBelch("%" PATH_FMT ": can't find section named: ", oc->fileName);
printName(sym->Name, strtab);
errorBelch(" in %s", secname);
return 0;
= (COFF_section*) myindex ( sizeof_COFF_section, sectab, sym->SectionNumber-1 );
S = ((size_t)(oc->image))
+ ((size_t)(section_sym->PointerToRawData))
+ ((size_t)(sym->Value));
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