capture_context_mac: Do what the comments say, and fix some comments

client/capture_context_mac.S

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 21 matching lines @@
   pushl %ebp
   .cfi_def_cfa_offset 8
   .cfi_offset %ebp, -8
   movl %esp, %ebp
   .cfi_def_cfa_register %ebp
 
   // Note that 16-byte stack alignment is not maintained because this function
   // does not call out to any other.
 
   // pushfl first, because some instructions (but probably none used here)
-  // affect %eflags. %eflags will be in -4(%rbp).
+  // affect %eflags. %eflags will be in -4(%ebp).
   pushfl
 
   // Save the original value of %eax, and use %eax to hold the x86_thread_state*
-  // argument. The original value of %eax will be in -8(%rbp).
+  // argument. The original value of %eax will be in -8(%ebp).
   pushl %eax
   movl 8(%ebp), %eax
 
   // Initialize the header identifying the x86_thread_state_t structure as
   // carrying an x86_thread_state32_t (flavor x86_THREAD_STATE32) of size
   // x86_THREAD_STATE32_COUNT 32-bit values.
   movl $1, (%eax)  // x86_thread_state->tsh.flavor
   movl $16, 4(%eax)  // x86_thread_state->tsh.count
 
   // General-purpose registers whose values haven’t changed can be captured
@@ skipping 43 matching lines @@
   movw %es, %dx
   movl %edx, 60(%eax)  // x86_thread_state->uts.ts32.__es
   movw %fs, %dx
   movl %edx, 64(%eax)  // x86_thread_state->uts.ts32.__fs
   movw %gs, %dx
   movl %edx, 68(%eax)  // x86_thread_state->uts.ts32.__gs
 
   // Clean up by restoring clobbered registers, even those considered volatile
   // by the ABI, so that the captured context represents the state at this
   // function’s exit.
+  movl 20(%eax), %edx  // x86_thread_state->uts.ts32.__edx
   popl %eax
   popfl
 
   popl %ebp
 
   ret
 
   .cfi_endproc
 
 #elif defined(__x86_64__)
@@ skipping 88 matching lines @@
 
   ret
 
   .cfi_endproc
 
 #endif
 
 .subsections_via_symbols
 
 #endif