[libc-commits] [libc] [libc] Add barebones dl_iterate_phdr implementation (PR #194196)

[Jeff Bailey via libc-commits]

================
@@ -8,18 +8,61 @@
 
 #include "dl_iterate_phdr.h"
 
+#include "llvm-libc-macros/link-macros.h"
+#include "src/__support/OSUtil/linux/auxv.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
 
+#include <elf.h>
+
+extern "C" void *__executable_start;
+
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(int, dl_iterate_phdr,
                    (__dl_iterate_phdr_callback_t callback, void *arg)) {
-  // FIXME: For pure static linking, this can report just the executable with
-  // info from __ehdr_start or AT_{PHDR,PHNUM} decoding, and its PT_TLS; and it
-  // could report the vDSO.
-  (void)callback, (void)arg;
-  return 0;
+  ElfW(Ehdr) *executable_header =
+      reinterpret_cast<ElfW(Ehdr) *>(&__executable_start);
+  struct dl_phdr_info executable_info;
+  executable_info.dlpi_addr = 0;
+  executable_info.dlpi_name = nullptr;
+  executable_info.dlpi_phdr = reinterpret_cast<ElfW(Phdr) *>(
+      reinterpret_cast<uintptr_t>(executable_header) +
+      executable_header->e_phoff);
+  executable_info.dlpi_phnum = executable_header->e_phnum;
+  executable_info.dlpi_adds = 0;
+  executable_info.dlpi_subs = 0;
+  executable_info.dlpi_tls_modid = 0;
+  executable_info.dlpi_tls_data = nullptr;
+  int executable_return_code =
+      callback(&executable_info, sizeof(executable_info), arg);
+  if (executable_return_code != 0)
+    return executable_return_code;
+
+  cpp::optional<unsigned long> vdso_start_address =
+      LIBC_NAMESPACE::auxv::get(AT_SYSINFO_EHDR);
----------------
kaladron wrote:

```suggestion
      auxv::get(AT_SYSINFO_EHDR);
```

https://github.com/llvm/llvm-project/pull/194196