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hot code swapping PoC working

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- improve fn prototypes of process_vm_writev
 - make the memory writable in the ELF file
 - force the linker to always append the function
 - write updates with process_vm_writev
This commit is contained in:
Andrew Kelley 2022-01-21 18:47:29 -07:00
parent 50a2bb58d2
commit 4f4ddf5ef2
2 changed files with 48 additions and 13 deletions
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20
lib/std/os/linux.zig
View File

@ -1716,26 +1716,26 @@ pub fn pidfd_send_signal(pidfd: fd_t, sig: i32, info: ?*siginfo_t, flags: u32) u
);
}
pub fn process_vm_readv(pid: pid_t, local: [*]const iovec, local_count: usize, remote: [*]const iovec, remote_count: usize, flags: usize) usize {
pub fn process_vm_readv(pid: pid_t, local: []iovec, remote: []const iovec_const, flags: usize) usize {
return syscall6(
.process_vm_readv,
@bitCast(usize, @as(isize, pid)),
@ptrToInt(local),
local_count,
@ptrToInt(remote),
remote_count,
@ptrToInt(local.ptr),
local.len,
@ptrToInt(remote.ptr),
remote.len,
flags,
);
}
pub fn process_vm_writev(pid: pid_t, local: [*]const iovec, local_count: usize, remote: [*]const iovec, remote_count: usize, flags: usize) usize {
pub fn process_vm_writev(pid: pid_t, local: []const iovec_const, remote: []const iovec_const, flags: usize) usize {
return syscall6(
.process_vm_writev,
@bitCast(usize, @as(isize, pid)),
@ptrToInt(local),
local_count,
@ptrToInt(remote),
remote_count,
@ptrToInt(local.ptr),
local.len,
@ptrToInt(remote.ptr),
remote.len,
flags,
);
}

41
src/link/Elf.zig
View File

@ -467,7 +467,7 @@ pub fn populateMissingMetadata(self: *Elf) !void {
.p_paddr = entry_addr,
.p_memsz = file_size,
.p_align = p_align,
.p_flags = elf.PF_X | elf.PF_R,
.p_flags = elf.PF_X | elf.PF_R | elf.PF_W,
});
self.entry_addr = null;
self.phdr_table_dirty = true;
@ -493,7 +493,7 @@ pub fn populateMissingMetadata(self: *Elf) !void {
.p_paddr = got_addr,
.p_memsz = file_size,
.p_align = p_align,
.p_flags = elf.PF_R,
.p_flags = elf.PF_R | elf.PF_W,
});
self.phdr_table_dirty = true;
}
@ -516,7 +516,7 @@ pub fn populateMissingMetadata(self: *Elf) !void {
.p_paddr = rodata_addr,
.p_memsz = file_size,
.p_align = p_align,
.p_flags = elf.PF_R,
.p_flags = elf.PF_R | elf.PF_W,
});
self.phdr_table_dirty = true;
}
@ -2451,6 +2451,23 @@ fn updateDeclCode(self: *Elf, decl_index: Module.Decl.Index, code: []const u8, s
const phdr_index = self.sections.items(.phdr_index)[shdr_index];
const section_offset = local_sym.st_value - self.program_headers.items[phdr_index].p_vaddr;
const file_offset = self.sections.items(.shdr)[shdr_index].sh_offset + section_offset;
if (self.base.child_pid) |pid| {
var code_vec: [1]std.os.iovec_const = .{.{
.iov_base = code.ptr,
.iov_len = code.len,
}};
var remote_vec: [1]std.os.iovec_const = .{.{
.iov_base = @intToPtr([*]u8, local_sym.st_value),
.iov_len = code.len,
}};
const rc = std.os.linux.process_vm_writev(pid, &code_vec, &remote_vec, 0);
switch (std.os.errno(rc)) {
.SUCCESS => assert(rc == code.len),
else => |errno| log.warn("process_vm_writev failure: {s}", .{@tagName(errno)}),
}
}
try self.base.file.?.pwriteAll(code, file_offset);
return local_sym;
@ -2820,6 +2837,8 @@ fn writeOffsetTableEntry(self: *Elf, index: usize) !void {
const endian = self.base.options.target.cpu.arch.endian();
const shdr = &self.sections.items(.shdr)[self.got_section_index.?];
const off = shdr.sh_offset + @as(u64, entry_size) * index;
const phdr = &self.program_headers.items[self.phdr_got_index.?];
const vaddr = phdr.p_vaddr + @as(u64, entry_size) * index;
switch (entry_size) {
2 => {
var buf: [2]u8 = undefined;
@ -2835,6 +2854,22 @@ fn writeOffsetTableEntry(self: *Elf, index: usize) !void {
var buf: [8]u8 = undefined;
mem.writeInt(u64, &buf, self.offset_table.items[index], endian);
try self.base.file.?.pwriteAll(&buf, off);
if (self.base.child_pid) |pid| {
var local_vec: [1]std.os.iovec_const = .{.{
.iov_base = &buf,
.iov_len = buf.len,
}};
var remote_vec: [1]std.os.iovec_const = .{.{
.iov_base = @intToPtr([*]u8, vaddr),
.iov_len = buf.len,
}};
const rc = std.os.linux.process_vm_writev(pid, &local_vec, &remote_vec, 0);
switch (std.os.errno(rc)) {
.SUCCESS => assert(rc == buf.len),
else => |errno| log.warn("process_vm_writev failure: {s}", .{@tagName(errno)}),
}
}
},
else => unreachable,
}