Commit 4f4ddf5ef2f2e2ee2774e0a5311b099ea19d9ce2 | zig

author	Andrew Kelley <andrew@ziglang.org> 2022-01-21 18:47:29-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2023-03-15 10:48:12-07:00
log	4f4ddf5ef2f2e2ee2774e0a5311b099ea19d9ce2
tree	5a57b5870be7d3e1bb9eea8a1350930d525b02ab
parent	50a2bb58d23a686f52b389c062f0299cc2a5f8ed

hot code swapping PoC working

 - 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

2 files changed, 48 insertions(+), 13 deletions(-)

lib
- std
  - os
    linux.zig
src
- link
  - Elf.zig

lib/std/os/linux.zig+10-10

...	...	@@ -1716,26 +1716,26 @@ pub fn pidfd_send_signal(pidfd: fd_t, sig: i32, info: ?*siginfo_t, flags: u32) u
1716	1716	);
1717	1717	}
1718	1718
1719		pub fn process_vm_readv(pid: pid_t, local: []const iovec, local_count: usize, remote: []const iovec, remote_count: usize, flags: usize) usize {
	1719	pub fn process_vm_readv(pid: pid_t, local: []iovec, remote: []const iovec_const, flags: usize) usize {
1720	1720	return syscall6(
1721	1721	.process_vm_readv,
1722	1722	@bitCast(usize, @as(isize, pid)),
1723		@ptrToInt(local),
1724		local_count,
1725		@ptrToInt(remote),
1726		remote_count,
	1723	@ptrToInt(local.ptr),
	1724	local.len,
	1725	@ptrToInt(remote.ptr),
	1726	remote.len,
1727	1727	flags,
1728	1728	);
1729	1729	}
1730	1730
1731		pub fn process_vm_writev(pid: pid_t, local: []const iovec, local_count: usize, remote: []const iovec, remote_count: usize, flags: usize) usize {
	1731	pub fn process_vm_writev(pid: pid_t, local: []const iovec_const, remote: []const iovec_const, flags: usize) usize {
1732	1732	return syscall6(
1733	1733	.process_vm_writev,
1734	1734	@bitCast(usize, @as(isize, pid)),
1735		@ptrToInt(local),
1736		local_count,
1737		@ptrToInt(remote),
1738		remote_count,
	1735	@ptrToInt(local.ptr),
	1736	local.len,
	1737	@ptrToInt(remote.ptr),
	1738	remote.len,
1739	1739	flags,
1740	1740	);
1741	1741	}

src/link/Elf.zig+38-3

...	...	@@ -467,7 +467,7 @@ pub fn populateMissingMetadata(self: *Elf) !void {
467	467	.p_paddr = entry_addr,
468	468	.p_memsz = file_size,
469	469	.p_align = p_align,
470		.p_flags = elf.PF_X \| elf.PF_R,
	470	.p_flags = elf.PF_X \| elf.PF_R \| elf.PF_W,
471	471	});
472	472	self.entry_addr = null;
473	473	self.phdr_table_dirty = true;
...	...	@@ -493,7 +493,7 @@ pub fn populateMissingMetadata(self: *Elf) !void {
493	493	.p_paddr = got_addr,
494	494	.p_memsz = file_size,
495	495	.p_align = p_align,
496		.p_flags = elf.PF_R,
	496	.p_flags = elf.PF_R \| elf.PF_W,
497	497	});
498	498	self.phdr_table_dirty = true;
499	499	}
...	...	@@ -516,7 +516,7 @@ pub fn populateMissingMetadata(self: *Elf) !void {
516	516	.p_paddr = rodata_addr,
517	517	.p_memsz = file_size,
518	518	.p_align = p_align,
519		.p_flags = elf.PF_R,
	519	.p_flags = elf.PF_R \| elf.PF_W,
520	520	});
521	521	self.phdr_table_dirty = true;
522	522	}
...	...	@@ -2451,6 +2451,23 @@ fn updateDeclCode(self: *Elf, decl_index: Module.Decl.Index, code: []const u8, s
2451	2451	const phdr_index = self.sections.items(.phdr_index)[shdr_index];
2452	2452	const section_offset = local_sym.st_value - self.program_headers.items[phdr_index].p_vaddr;
2453	2453	const file_offset = self.sections.items(.shdr)[shdr_index].sh_offset + section_offset;
	2454
	2455	if (self.base.child_pid) \|pid\| {
	2456	var code_vec: [1]std.os.iovec_const = .{.{
	2457	.iov_base = code.ptr,
	2458	.iov_len = code.len,
	2459	}};
	2460	var remote_vec: [1]std.os.iovec_const = .{.{
	2461	.iov_base = @intToPtr([*]u8, local_sym.st_value),
	2462	.iov_len = code.len,
	2463	}};
	2464	const rc = std.os.linux.process_vm_writev(pid, &code_vec, &remote_vec, 0);
	2465	switch (std.os.errno(rc)) {
	2466	.SUCCESS => assert(rc == code.len),
	2467	else => \|errno\| log.warn("process_vm_writev failure: {s}", .{@tagName(errno)}),
	2468	}
	2469	}
	2470
2454	2471	try self.base.file.?.pwriteAll(code, file_offset);
2455	2472
2456	2473	return local_sym;
...	...	@@ -2820,6 +2837,8 @@ fn writeOffsetTableEntry(self: *Elf, index: usize) !void {
2820	2837	const endian = self.base.options.target.cpu.arch.endian();
2821	2838	const shdr = &self.sections.items(.shdr)[self.got_section_index.?];
2822	2839	const off = shdr.sh_offset + @as(u64, entry_size) * index;
	2840	const phdr = &self.program_headers.items[self.phdr_got_index.?];
	2841	const vaddr = phdr.p_vaddr + @as(u64, entry_size) * index;
2823	2842	switch (entry_size) {
2824	2843	2 => {
2825	2844	var buf: [2]u8 = undefined;
...	...	@@ -2835,6 +2854,22 @@ fn writeOffsetTableEntry(self: *Elf, index: usize) !void {
2835	2854	var buf: [8]u8 = undefined;
2836	2855	mem.writeInt(u64, &buf, self.offset_table.items[index], endian);
2837	2856	try self.base.file.?.pwriteAll(&buf, off);
	2857
	2858	if (self.base.child_pid) \|pid\| {
	2859	var local_vec: [1]std.os.iovec_const = .{.{
	2860	.iov_base = &buf,
	2861	.iov_len = buf.len,
	2862	}};
	2863	var remote_vec: [1]std.os.iovec_const = .{.{
	2864	.iov_base = @intToPtr([*]u8, vaddr),
	2865	.iov_len = buf.len,
	2866	}};
	2867	const rc = std.os.linux.process_vm_writev(pid, &local_vec, &remote_vec, 0);
	2868	switch (std.os.errno(rc)) {
	2869	.SUCCESS => assert(rc == buf.len),
	2870	else => \|errno\| log.warn("process_vm_writev failure: {s}", .{@tagName(errno)}),
	2871	}
	2872	}
2838	2873	},
2839	2874	else => unreachable,
2840	2875	}