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Elf2: incrementally update object relocs
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+105
-34
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1 file changed

+105
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‎src/link/Elf2.zig‎

Lines changed: 105 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -164,7 +164,26 @@ pub const Node = union(enum) {
164164
}
165165
};
166166

167-
pub const Section = struct { si: Symbol.Index, rela_si: Symbol.Index };
167+
pub const Section = struct {
168+
si: Symbol.Index,
169+
rela_si: Symbol.Index,
170+
rela_free: RelIndex,
171+
172+
pub const RelIndex = enum(u32) {
173+
none,
174+
_,
175+
176+
pub fn wrap(i: ?u32) RelIndex {
177+
return @enumFromInt((i orelse return .none) + 1);
178+
}
179+
pub fn unwrap(ri: RelIndex) ?u32 {
180+
return switch (ri) {
181+
.none => null,
182+
else => @intFromEnum(ri) - 1,
183+
};
184+
}
185+
};
186+
};
168187

169188
pub const StringTable = struct {
170189
map: std.HashMapUnmanaged(u32, void, StringTable.Context, std.hash_map.default_max_load_percentage),
@@ -462,7 +481,7 @@ pub const Reloc = extern struct {
462481
next: Reloc.Index,
463482
loc: Symbol.Index,
464483
target: Symbol.Index,
465-
rel_index: u32,
484+
index: Section.RelIndex,
466485
offset: u64,
467486
addend: i64,
468487

@@ -472,6 +491,16 @@ pub const Reloc = extern struct {
472491
RISCV: std.elf.R_RISCV,
473492
PPC64: std.elf.R_PPC64,
474493

494+
pub fn none(elf: *Elf) Reloc.Type {
495+
return switch (elf.ehdrField(.machine)) {
496+
else => unreachable,
497+
.AARCH64 => .{ .AARCH64 = .NONE },
498+
.PPC64 => .{ .PPC64 = .NONE },
499+
.RISCV => .{ .RISCV = .NONE },
500+
.X86_64 => .{ .X86_64 = .NONE },
501+
};
502+
}
503+
475504
pub fn absAddr(elf: *Elf) Reloc.Type {
476505
return switch (elf.ehdrField(.machine)) {
477506
else => unreachable,
@@ -481,12 +510,35 @@ pub const Reloc = extern struct {
481510
.X86_64 => .{ .X86_64 = .@"64" },
482511
};
483512
}
513+
484514
pub fn sizeAddr(elf: *Elf) Reloc.Type {
485515
return switch (elf.ehdrField(.machine)) {
486516
else => unreachable,
487517
.X86_64 => .{ .X86_64 = .SIZE64 },
488518
};
489519
}
520+
521+
pub fn wrap(int: u32, elf: *Elf) Reloc.Type {
522+
return switch (elf.ehdrField(.machine)) {
523+
else => unreachable,
524+
inline .AARCH64,
525+
.PPC64,
526+
.RISCV,
527+
.X86_64,
528+
=> |machine| @unionInit(Reloc.Type, @tagName(machine), @enumFromInt(int)),
529+
};
530+
}
531+
532+
pub fn unwrap(rt: Reloc.Type, elf: *Elf) u32 {
533+
return switch (elf.ehdrField(.machine)) {
534+
else => unreachable,
535+
inline .AARCH64,
536+
.PPC64,
537+
.RISCV,
538+
.X86_64,
539+
=> |machine| @intFromEnum(@field(rt, @tagName(machine))),
540+
};
541+
}
490542
};
491543

492544
pub const Index = enum(u32) {
@@ -590,6 +642,32 @@ pub const Reloc = extern struct {
590642
.none => {},
591643
else => |next| next.get(elf).prev = reloc.prev,
592644
}
645+
switch (elf.ehdrField(.type)) {
646+
.NONE, .CORE, _ => unreachable,
647+
.REL => {
648+
const sh = reloc.loc.shndx(elf).get(elf);
649+
switch (elf.shdrPtr(sh.rela_si.shndx(elf))) {
650+
inline else => |shdr, class| {
651+
const Rela = class.ElfN().Rela;
652+
const ent_size = elf.targetLoad(&shdr.entsize);
653+
const start = ent_size * reloc.index.unwrap().?;
654+
const rela: *Rela = @ptrCast(@alignCast(
655+
sh.rela_si.node(elf).slice(&elf.mf)[start..][0..ent_size],
656+
));
657+
rela.* = .{
658+
.offset = @intFromEnum(sh.rela_free),
659+
.info = .{
660+
.type = @intCast(Reloc.Type.none(elf).unwrap(elf)),
661+
.sym = 0,
662+
},
663+
.addend = 0,
664+
};
665+
},
666+
}
667+
sh.rela_free = reloc.index;
668+
},
669+
.EXEC, .DYN => assert(reloc.index == .none),
670+
}
593671
reloc.* = undefined;
594672
}
595673

@@ -1036,7 +1114,7 @@ fn initHeaders(
10361114
.entsize = 0,
10371115
};
10381116
if (target_endian != native_endian) std.mem.byteSwapAllFields(ElfN.Shdr, sh_undef);
1039-
elf.shdrs.appendAssumeCapacity(.{ .si = .null, .rela_si = .null });
1117+
elf.shdrs.appendAssumeCapacity(.{ .si = .null, .rela_si = .null, .rela_free = .none });
10401118

10411119
try elf.symtab.ensureTotalCapacity(gpa, 1);
10421120
elf.symtab.addOneAssumeCapacity().* = .{
@@ -1880,18 +1958,7 @@ fn loadObject(
18801958
rel.offset - loc_sec.shdr.addr,
18811959
target_si,
18821960
rel.addend,
1883-
switch (elf.ehdrField(.machine)) {
1884-
else => unreachable,
1885-
inline .AARCH64,
1886-
.PPC64,
1887-
.RISCV,
1888-
.X86_64,
1889-
=> |machine| @unionInit(
1890-
Reloc.Type,
1891-
@tagName(machine),
1892-
@enumFromInt(rel.info.type),
1893-
),
1894-
},
1961+
.wrap(rel.info.type, elf),
18951962
);
18961963
}
18971964
},
@@ -2156,7 +2223,7 @@ fn addSection(elf: *Elf, segment_ni: MappedFile.Node.Index, opts: struct {
21562223
});
21572224
const si = elf.addSymbolAssumeCapacity();
21582225
elf.nodes.appendAssumeCapacity(.{ .section = si });
2159-
elf.shdrs.appendAssumeCapacity(.{ .si = si, .rela_si = .null });
2226+
elf.shdrs.appendAssumeCapacity(.{ .si = si, .rela_si = .null, .rela_free = .none });
21602227
si.get(elf).ni = ni;
21612228
const addr = elf.computeNodeVAddr(ni);
21622229
const offset = ni.fileLocation(&elf.mf, false).offset;
@@ -2275,39 +2342,43 @@ pub fn addRelocAssumeCapacity(
22752342
.next = target.target_relocs,
22762343
.loc = loc_si,
22772344
.target = target_si,
2278-
.rel_index = switch (elf.ehdrField(.type)) {
2345+
.index = index: switch (elf.ehdrField(.type)) {
22792346
.NONE, .CORE, _ => unreachable,
2280-
.REL => rel_index: {
2281-
const rela_si = loc_si.shndx(elf).get(elf).rela_si;
2282-
switch (elf.shdrPtr(rela_si.shndx(elf))) {
2347+
.REL => {
2348+
const sh = loc_si.shndx(elf).get(elf);
2349+
switch (elf.shdrPtr(sh.rela_si.shndx(elf))) {
22832350
inline else => |shdr, class| {
22842351
const Rela = class.ElfN().Rela;
2285-
const old_size = elf.targetLoad(&shdr.size);
22862352
const ent_size = elf.targetLoad(&shdr.entsize);
2287-
const new_size = old_size + ent_size;
2288-
elf.targetStore(&shdr.size, @intCast(new_size));
2289-
const rela: *Rela = @ptrCast(@alignCast(
2290-
rela_si.node(elf).slice(&elf.mf)[@intCast(old_size)..@intCast(new_size)],
2291-
));
2353+
const rela_slice = sh.rela_si.node(elf).slice(&elf.mf);
2354+
const index: u32 = if (sh.rela_free.unwrap()) |index| alloc_index: {
2355+
const rela: *Rela = @ptrCast(@alignCast(
2356+
sh.rela_si.node(elf).slice(&elf.mf)[ent_size * index ..][0..ent_size],
2357+
));
2358+
sh.rela_free = @enumFromInt(rela.offset);
2359+
break :alloc_index index;
2360+
} else alloc_index: {
2361+
const old_size = elf.targetLoad(&shdr.size);
2362+
const new_size = old_size + ent_size;
2363+
elf.targetStore(&shdr.size, @intCast(new_size));
2364+
break :alloc_index @intCast(@divExact(old_size, ent_size));
2365+
};
2366+
const rela: *Rela =
2367+
@ptrCast(@alignCast(rela_slice[ent_size * index ..][0..ent_size]));
22922368
rela.* = .{
22932369
.offset = @intCast(offset),
22942370
.info = .{
2295-
.type = switch (elf.ehdrField(.machine)) {
2296-
else => |machine| @panic(@tagName(machine)),
2297-
inline .X86_64, .AARCH64, .RISCV, .PPC64 => |machine| @intCast(
2298-
@intFromEnum(@field(@"type", @tagName(machine))),
2299-
),
2300-
},
2371+
.type = @intCast(@"type".unwrap(elf)),
23012372
.sym = @intCast(@intFromEnum(target_si)),
23022373
},
23032374
.addend = @intCast(addend),
23042375
};
23052376
if (elf.targetEndian() != native_endian) std.mem.byteSwapAllFields(Rela, rela);
2306-
break :rel_index @intCast(@divExact(old_size, ent_size));
2377+
break :index .wrap(index);
23072378
},
23082379
}
23092380
},
2310-
.EXEC, .DYN => 0,
2381+
.EXEC, .DYN => .none,
23112382
},
23122383
.offset = offset,
23132384
.addend = addend,

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