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Merge pull request #20823 from alexrp/start-pie-mips-ppc
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`std.os.linux.start_pie`: Add mips and powerpc support
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@andrewrk
andrewrk authored Aug 1, 2024
2 parents 63aa85e + 2e719f3 commit 9c22a6b
Showing 1 changed file with 105 additions and 20 deletions.
125 changes: 105 additions & 20 deletions lib/std/os/linux/start_pie.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@ const R_CSKY_RELATIVE = 9;
const R_HEXAGON_RELATIVE = 35;
const R_LARCH_RELATIVE = 3;
const R_68K_RELATIVE = 22;
const R_MIPS_RELATIVE = 128;
const R_PPC_RELATIVE = 22;
const R_RISCV_RELATIVE = 3;
const R_390_RELATIVE = 12;
const R_SPARC_RELATIVE = 22;
Expand All @@ -26,6 +28,8 @@ const R_RELATIVE = switch (builtin.cpu.arch) {
.hexagon => R_HEXAGON_RELATIVE,
.loongarch32, .loongarch64 => R_LARCH_RELATIVE,
.m68k => R_68K_RELATIVE,
.mips, .mipsel, .mips64, .mips64el => R_MIPS_RELATIVE,
.powerpc, .powerpcle, .powerpc64, .powerpc64le => R_PPC_RELATIVE,
.riscv32, .riscv64 => R_RISCV_RELATIVE,
.s390x => R_390_RELATIVE,
else => @compileError("Missing R_RELATIVE definition for this target"),
Expand All @@ -34,7 +38,7 @@ const R_RELATIVE = switch (builtin.cpu.arch) {
// Obtain a pointer to the _DYNAMIC array.
// We have to compute its address as a PC-relative quantity not to require a
// relocation that, at this point, is not yet applied.
fn getDynamicSymbol() [*]elf.Dyn {
inline fn getDynamicSymbol() [*]elf.Dyn {
return switch (builtin.cpu.arch) {
.x86 => asm volatile (
\\ .weak _DYNAMIC
Expand Down Expand Up @@ -111,6 +115,57 @@ fn getDynamicSymbol() [*]elf.Dyn {
\\ lea (%[ret], %%pc), %[ret]
: [ret] "=r" (-> [*]elf.Dyn),
),
.mips, .mipsel => asm volatile (
\\ .weak _DYNAMIC
\\ .hidden _DYNAMIC
\\ bal 1f
\\ .gpword _DYNAMIC
\\ 1:
\\ lw %[ret], 0($ra)
\\ addu %[ret], %[ret], $gp
: [ret] "=r" (-> [*]elf.Dyn),
:
: "lr"
),
.mips64, .mips64el => asm volatile (
\\ .weak _DYNAMIC
\\ .hidden _DYNAMIC
\\ .balign 8
\\ bal 1f
\\ .gpdword _DYNAMIC
\\ 1:
\\ ld %[ret], 0($ra)
\\ daddu %[ret], %[ret], $gp
: [ret] "=r" (-> [*]elf.Dyn),
:
: "lr"
),
.powerpc, .powerpcle => asm volatile (
\\ .weak _DYNAMIC
\\ .hidden _DYNAMIC
\\ bl 1f
\\ .long _DYNAMIC - .
\\ 1:
\\ mflr %[ret]
\\ lwz 4, 0(%[ret])
\\ add %[ret], 4, %[ret]
: [ret] "=r" (-> [*]elf.Dyn),
:
: "lr", "r4"
),
.powerpc64, .powerpc64le => asm volatile (
\\ .weak _DYNAMIC
\\ .hidden _DYNAMIC
\\ bl 1f
\\ .quad _DYNAMIC - .
\\ 1:
\\ mflr %[ret]
\\ ld 4, 0(%[ret])
\\ add %[ret], 4, %[ret]
: [ret] "=r" (-> [*]elf.Dyn),
:
: "lr", "r4"
),
.riscv32, .riscv64 => asm volatile (
\\ .weak _DYNAMIC
\\ .hidden _DYNAMIC
Expand All @@ -121,9 +176,9 @@ fn getDynamicSymbol() [*]elf.Dyn {
\\ .weak _DYNAMIC
\\ .hidden _DYNAMIC
\\ larl %[ret], 1f
\\ agf %[ret], 0(%[ret])
\\ ag %[ret], 0(%[ret])
\\ b 2f
\\ 1: .long _DYNAMIC - .
\\ 1: .quad _DYNAMIC - .
\\ 2:
: [ret] "=r" (-> [*]elf.Dyn),
),
Expand All @@ -138,6 +193,7 @@ pub fn relocate(phdrs: []elf.Phdr) void {
@disableInstrumentation();

const dynv = getDynamicSymbol();

// Recover the delta applied by the loader by comparing the effective and
// the theoretical load addresses for the `_DYNAMIC` symbol.
const base_addr = base: {
Expand All @@ -149,34 +205,63 @@ pub fn relocate(phdrs: []elf.Phdr) void {
@trap();
};

var rel_addr: usize = 0;
var rela_addr: usize = 0;
var rel_size: usize = 0;
var rela_size: usize = 0;
var sorted_dynv: [elf.DT_NUM]elf.Addr = undefined;

// Zero-initialized this way to prevent the compiler from turning this into
// `memcpy` or `memset` calls (which can require relocations).
for (&sorted_dynv) |*dyn| {
const pdyn: *volatile elf.Addr = @ptrCast(dyn);
pdyn.* = 0;
}

{
// `dynv` has no defined order. Fix that.
var i: usize = 0;
while (dynv[i].d_tag != elf.DT_NULL) : (i += 1) {
switch (dynv[i].d_tag) {
elf.DT_REL => rel_addr = base_addr + dynv[i].d_val,
elf.DT_RELA => rela_addr = base_addr + dynv[i].d_val,
elf.DT_RELSZ => rel_size = dynv[i].d_val,
elf.DT_RELASZ => rela_size = dynv[i].d_val,
else => {},
if (dynv[i].d_tag < elf.DT_NUM) sorted_dynv[@bitCast(dynv[i].d_tag)] = dynv[i].d_val;
}
}

// Deal with the GOT relocations that MIPS uses first.
if (builtin.cpu.arch.isMIPS()) {
const count: elf.Addr = blk: {
// This is an architecture-specific tag, so not part of `sorted_dynv`.
var i: usize = 0;
while (dynv[i].d_tag != elf.DT_NULL) : (i += 1) {
if (dynv[i].d_tag == elf.DT_MIPS_LOCAL_GOTNO) break :blk dynv[i].d_val;
}

break :blk 0;
};

const got: [*]usize = @ptrFromInt(base_addr + sorted_dynv[elf.DT_PLTGOT]);

for (0..count) |i| {
got[i] += base_addr;
}
}

// Apply the relocations.
if (rel_addr != 0) {
const rel = std.mem.bytesAsSlice(elf.Rel, @as([*]u8, @ptrFromInt(rel_addr))[0..rel_size]);
for (rel) |r| {
// Apply normal relocations.

const rel = sorted_dynv[elf.DT_REL];
if (rel != 0) {
const rels = @call(.always_inline, std.mem.bytesAsSlice, .{
elf.Rel,
@as([*]u8, @ptrFromInt(base_addr + rel))[0..sorted_dynv[elf.DT_RELSZ]],
});
for (rels) |r| {
if (r.r_type() != R_RELATIVE) continue;
@as(*usize, @ptrFromInt(base_addr + r.r_offset)).* += base_addr;
}
}
if (rela_addr != 0) {
const rela = std.mem.bytesAsSlice(elf.Rela, @as([*]u8, @ptrFromInt(rela_addr))[0..rela_size]);
for (rela) |r| {

const rela = sorted_dynv[elf.DT_RELA];
if (rela != 0) {
const relas = @call(.always_inline, std.mem.bytesAsSlice, .{
elf.Rela,
@as([*]u8, @ptrFromInt(base_addr + rela))[0..sorted_dynv[elf.DT_RELASZ]],
});
for (relas) |r| {
if (r.r_type() != R_RELATIVE) continue;
@as(*usize, @ptrFromInt(base_addr + r.r_offset)).* = base_addr + @as(usize, @bitCast(r.r_addend));
}
Expand Down

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