gdb: use std::vector instead of alloca in core_target::get_core_register_section

As I was trying to compile gdb for an m68k host, I got this error:

  CXX    corelow.o
In file included from /binutils-gdb/gdb/gdbsupport/common-defs.h:120,
                 from /binutils-gdb/gdb/defs.h:28,
                 from /binutils-gdb/gdb/corelow.c:20:
/binutils-gdb/gdb/corelow.c: In member function 'void core_target::get_core_register_section(regcache*, const regset*, const char*, int, int, const char*, bool)':
/binutils-gdb/gdb/../include/libiberty.h:727:36: error: 'alloca' bound is unknown [-Werror=alloca-larger-than=]
  727 | # define alloca(x) __builtin_alloca(x)
      |                    ~~~~~~~~~~~~~~~~^~~
/binutils-gdb/gdb/corelow.c:625:23: note: in expansion of macro 'alloca'
  625 |   contents = (char *) alloca (size);
      |                       ^~~~~~

We are using alloca to hold the contents of a the core register
sections.  These sections are typically fairly small, but there is no
realy guarantee, so I think it would be more reasonable to just use
dynamic allocation here.

gdb/ChangeLog:

	* corelow.c (core_target::get_core_register_section): Use
	  std::vector instead of alloca.

1 files changed, 5 insertions, 6 deletions

diff --git a/gdb/corelow.c b/gdb/corelow.c
index f162a1b..0418ec2 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -594,7 +594,6 @@ core_target::get_core_register_section (struct regcache *regcache,
 {
   struct bfd_section *section;
   bfd_size_type size;
-  char *contents;
   bool variable_size_section = (regset != NULL
 				&& regset->flags & REGSET_VARIABLE_SIZE);
 
@@ -622,9 +621,9 @@ core_target::get_core_register_section (struct regcache *regcache,
 	       section_name.c_str ());
     }
 
-  contents = (char *) alloca (size);
-  if (! bfd_get_section_contents (core_bfd, section, contents,
-				  (file_ptr) 0, size))
+  std::vector<char> contents (size);
+  if (!bfd_get_section_contents (core_bfd, section, contents.data (),
+				 (file_ptr) 0, size))
     {
       warning (_("Couldn't read %s registers from `%s' section in core file."),
 	       human_name, section_name.c_str ());
@@ -633,12 +632,12 @@ core_target::get_core_register_section (struct regcache *regcache,
 
   if (regset != NULL)
     {
-      regset->supply_regset (regset, regcache, -1, contents, size);
+      regset->supply_regset (regset, regcache, -1, contents.data (), size);
       return;
     }
 
   gdb_assert (m_core_vec != nullptr);
-  m_core_vec->core_read_registers (regcache, contents, size, which,
+  m_core_vec->core_read_registers (regcache, contents.data (), size, which,
 				   (CORE_ADDR) bfd_section_vma (section));
 }