Commit 3e22077d46a02d1c4e02dd603b560978dc184a87 | zig

author	LemonBoy <thatlemon@gmail.com> 2020-11-23 14:58:08+01:00
committer	LemonBoy <thatlemon@gmail.com> 2020-11-23 15:06:07+01:00
log	3e22077d46a02d1c4e02dd603b560978dc184a87
tree	471896cda055375d4c647e69c6ee2602665f4915
parent	0a84f85945a4d22c43b467c69ba7c26cd264659a

Fix the ELF base calculation

Find the effective ELF load address in dl_iterate_phdr by computing the
difference between the in-memory phdr and its p_vaddr specified in the
ELF file.

This makes the dl_iterate_phdr test pass and restores the stack traces.

3 files changed, 15 insertions(+), 8 deletions(-)

lib
- std
  - os.zig
  - os
    test.zig
  - process.zig

lib/std/os.zig+15-4

 @@ -4340,7 +4340,7 @@ pub fn dl_iterate_phdr(
     const elf_base = std.process.getBaseAddress();
     const ehdr = @intToPtr(*elf.Ehdr, elf_base);
-    // Make sure the base address points to an ELF image
+    // Make sure the base address points to an ELF image.
     assert(mem.eql(u8, ehdr.e_ident[0..4], "\x7fELF"));
     const n_phdr = ehdr.e_phnum;
     const phdrs = (@intToPtr([*]elf.Phdr, elf_base + ehdr.e_phoff))[0..n_phdr];
 @@ -4348,10 +4348,21 @@ pub fn dl_iterate_phdr(
     var it = dl.linkmap_iterator(phdrs) catch unreachable;
     // The executable has no dynamic link segment, create a single entry for
-    // the whole ELF image
+    // the whole ELF image.
     if (it.end()) {
+        // Find the base address for the ELF image, if this is a PIE the value
+        // is non-zero.
+        const base_address = for (phdrs) |*phdr| {
+            if (phdr.p_type == elf.PT_PHDR) {
+                break @ptrToInt(phdrs.ptr) - phdr.p_vaddr;
+                // We could try computing the difference between _DYNAMIC and
+                // the p_vaddr of the PT_DYNAMIC section, but using the phdr is
+                // good enough (Is it?).
+            }
+        } else unreachable;
         var info = dl_phdr_info{
-            .dlpi_addr = 0,
+            .dlpi_addr = base_address,
             .dlpi_name = "/proc/self/exe",
             .dlpi_phdr = phdrs.ptr,
             .dlpi_phnum = ehdr.e_phnum,
 @@ -4360,7 +4371,7 @@ pub fn dl_iterate_phdr(
         return callback(&info, @sizeOf(dl_phdr_info), context);
     }
-    // Last return value from the callback function
+    // Last return value from the callback function.
     while (it.next()) |entry| {
         var dlpi_phdr: [*]elf.Phdr = undefined;
         var dlpi_phnum: u16 = undefined;

lib/std/os/test.zig-2

...	@@ -386,8 +386,6 @@ fn iter_fn(info: dl_phdr_info, size: usize, counter: usize) IterFnError!void {	...	@@ -386,8 +386,6 @@ fn iter_fn(info: dl_phdr_info, size: usize, counter: usize) IterFnError!void {
386	test "dl_iterate_phdr" {	386	test "dl_iterate_phdr" {
387	if (builtin.os.tag == .windows or builtin.os.tag == .wasi or builtin.os.tag == .macos)	387	if (builtin.os.tag == .windows or builtin.os.tag == .wasi or builtin.os.tag == .macos)
388	return error.SkipZigTest;	388	return error.SkipZigTest;
389	if (builtin.position_independent_executable)
390	return error.SkipZigTest;
391		389
392	var counter: usize = 0;	390	var counter: usize = 0;
393	try os.dl_iterate_phdr(&counter, IterFnError, iter_fn);	391	try os.dl_iterate_phdr(&counter, IterFnError, iter_fn);

lib/std/process.zig-2

...	@@ -686,8 +686,6 @@ pub fn getBaseAddress() usize {	...	@@ -686,8 +686,6 @@ pub fn getBaseAddress() usize {
686	if (base != 0) {	686	if (base != 0) {
687	return base;	687	return base;
688	}	688	}
689	// XXX: Wrong for PIE executables, it should look at the difference
690	// between _DYNAMIC and the PT_DYNAMIC phdr instead.
691	const phdr = os.system.getauxval(std.elf.AT_PHDR);	689	const phdr = os.system.getauxval(std.elf.AT_PHDR);
692	return phdr - @sizeOf(std.elf.Ehdr);	690	return phdr - @sizeOf(std.elf.Ehdr);
693	},	691	},