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fix(elf): relocation records, DWARF tables and per-architecture frame data

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Assisted-by: GLM 5.3
This commit is contained in:
petrbalvin
2026-09-19 23:49:13 +02:00
parent ebdf14939f
commit f3c8510a58
11 changed files with 1302 additions and 164 deletions
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asm/elf_dwarf_sections.go
+84 -24
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@@ -3,6 +3,17 @@
package asm
import "encoding/binary"
// Absolute 64-bit relocation types for the DWARF address fixups, one per
// supported architecture (the numbers debug/elf carries).
const (
rX8664Abs64 = 1 // R_X86_64_64
rAARCH64Abs64 = 257 // R_AARCH64_ABS64
rRISCVAbs64 = 2 // R_RISCV_64
rLarchAbs64 = 2 // R_LARCH_64
)
// dwarfELFSections holds the laid-out DWARF sections ready for inclusion
// in an ELF file.
type dwarfELFSections struct {
@@ -11,15 +22,23 @@ type dwarfELFSections struct {
lineOff, lineSize int
lineStrOff, lineStrSize int
frameOff, frameSize int
// Relocations for .debug_info address references.
// .rela.debug_info and .rela.debug_line contents: file offsets and
// entry counts (zero count: the section is absent).
infoRelaOff, infoRelaCount int
lineRelaOff, lineRelaCount int
frameRelaOff, frameRelaCount int
// Relocations for .debug_info address references, offsets relative to
// the section start (what an r_offset in .rela.debug_info means).
infoRelocs []elfDwarfReloc
// Relocations for .debug_line address references.
// Relocations for .debug_line address references, section-relative.
lineRelocs []elfDwarfReloc
// Relocations for .debug_frame FDE initial locations, section-relative.
frameRelocs []elfDwarfReloc
}
type elfDwarfReloc struct {
off uint64
sym int // symbol index in .symtab
off uint64 // offset within the target section
sym int // symbol index in .symtab
addend int64
}
@@ -29,8 +48,9 @@ type elfDwarfReloc struct {
//
// symIdx maps function names to their .symtab indices (needed for relocations
// against .text symbols). The map uses objectName format (pkg.name); the
// DWARF code uses bare function names, so we build a reverse lookup.
func appendDWARFSections(out *[]byte, img *Image, srcFile string, symIdx map[string]int, align func(int)) *dwarfELFSections {
// DWARF code uses bare function names, so we build a reverse lookup. cfi
// carries the architecture's .debug_frame register conventions.
func appendDWARFSections(out *[]byte, img *Image, srcFile string, symIdx map[string]int, align func(int), cfi cfiArch) *dwarfELFSections {
// Build a lookup from bare function name to symbol index.
nameToIdx := make(map[string]int, len(symIdx))
for name, idx := range symIdx {
@@ -45,7 +65,7 @@ func appendDWARFSections(out *[]byte, img *Image, srcFile string, symIdx map[str
}
nameToIdx[name] = idx
}
ds := emitDWARF(img, srcFile)
ds := emitDWARF(img, srcFile, cfi)
if ds == nil || len(ds.debugAbbrev) == 0 {
return nil
}
@@ -68,15 +88,11 @@ func appendDWARFSections(out *[]byte, img *Image, srcFile string, symIdx map[str
align(1)
result.lineOff = len(*out)
result.lineSize = len(ds.debugLine)
lineBase := len(*out)
*out = append(*out, ds.debugLine...)
// Patch .debug_line relocations: replace placeholder addresses with
// actual .text offsets via symbol lookup.
for _, dr := range ds.lineRelocs {
if idx, ok := nameToIdx[dr.name]; ok {
result.lineRelocs = append(result.lineRelocs, elfDwarfReloc{
off: uint64(lineBase) + dr.off,
off: dr.off,
sym: idx,
addend: dr.addend,
})
@@ -87,33 +103,77 @@ func appendDWARFSections(out *[]byte, img *Image, srcFile string, symIdx map[str
align(1)
result.infoOff = len(*out)
result.infoSize = len(ds.debugInfo)
infoBase := len(*out)
*out = append(*out, ds.debugInfo...)
// .debug_frame
if len(ds.debugFrame) > 0 {
align(1)
result.frameOff = len(*out)
result.frameSize = len(ds.debugFrame)
*out = append(*out, ds.debugFrame...)
}
// Patch .debug_info relocations.
for _, dr := range ds.infoRelocs {
if idx, ok := nameToIdx[dr.name]; ok {
result.infoRelocs = append(result.infoRelocs, elfDwarfReloc{
off: uint64(infoBase) + dr.off,
off: dr.off,
sym: idx,
addend: dr.addend,
})
}
}
// .debug_frame: the section header declares alignment 8, so the data is
// padded to 8, matching it.
if len(ds.debugFrame) > 0 {
align(8)
result.frameOff = len(*out)
result.frameSize = len(ds.debugFrame)
*out = append(*out, ds.debugFrame...)
for _, dr := range ds.frameRelocs {
if idx, ok := nameToIdx[dr.name]; ok {
result.frameRelocs = append(result.frameRelocs, elfDwarfReloc{
off: dr.off,
sym: idx,
addend: dr.addend,
})
}
}
}
return result
}
// appendDWARFRelas writes the .rela.debug_info and .rela.debug_line section
// bodies from the relocations appendDWARFSections recorded, with the
// architecture's absolute 64-bit relocation type, and records their file
// offsets and entry counts on dw. Called after the DWARF sections
// themselves so the r_offsets (section-relative) need no adjustment.
func appendDWARFRelas(out *[]byte, dw *dwarfELFSections, abs64 uint32, align func(int)) {
le := binary.LittleEndian
write := func(relas []elfDwarfReloc) (off, count int) {
if len(relas) == 0 {
return 0, 0
}
align(8)
off = len(*out)
for _, r := range relas {
var b [24]byte
le.PutUint64(b[0:], r.off)
le.PutUint64(b[8:], uint64(r.sym)<<32|uint64(abs64))
le.PutUint64(b[16:], uint64(r.addend))
*out = append(*out, b[:]...)
}
return off, len(relas)
}
dw.infoRelaOff, dw.infoRelaCount = write(dw.infoRelocs)
dw.lineRelaOff, dw.lineRelaCount = write(dw.lineRelocs)
dw.frameRelaOff, dw.frameRelaCount = write(dw.frameRelocs)
}
// dwarfSourceName returns the source name the DWARF sections record: the
// image's source path when the assembler captured one, "gasm.s" otherwise.
func dwarfSourceName(img *Image) string {
if img.SourcePath != "" {
return img.SourcePath
}
return "gasm.s"
}
// dwarfSectionNames returns the DWARF section names for the string table.
var dwarfSectionNames = []string{
".debug_abbrev", ".debug_info", ".debug_line", ".debug_line_str",
".debug_frame", ".rela.debug_info", ".rela.debug_line",
".rela.debug_frame",
}