[PATCH] gcore: Query auxv for AT_PAGESZ in gcore_copy_callback

[Kevin Buettner <kevinb@redhat.com>]

This is a followup patch to commit c1da013915e, titled "gcore:  Handle
unreadable pages within readable memory regions".

In his review of that earlier patch, Tom de Vries recommended using
target_auxv_search with AT_PAGESZ to find the page size if it's
available; this patch implements that suggestion.  As before, a 4k
fallback size is used should the search for an AT_PAGESZ value not
succeed.
---
 gdb/gcore.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/gdb/gcore.c b/gdb/gcore.c
index 7bf2f00e866..66a9f6c4153 100644
--- a/gdb/gcore.c
+++ b/gdb/gcore.c
@@ -36,6 +36,7 @@
 #include "gdbsupport/gdb_unlinker.h"
 #include "gdbsupport/byte-vector.h"
 #include "gdbsupport/scope-exit.h"
+#include "auxv.h"
 
 /* To generate sparse cores, we look at the data to write in chunks of
    this size when considering whether to skip the write.  Only if we
@@ -766,6 +767,11 @@ gcore_copy_callback (bfd *obfd, asection *osec)
   size = std::min (total_size, (bfd_size_type) MAX_COPY_BYTES);
   gdb::byte_vector memhunk (size);
 
+  bfd_size_type page_size = FALLBACK_PAGE_SIZE;
+  CORE_ADDR at_pagesz;
+  if (target_auxv_search (AT_PAGESZ, &at_pagesz) > 0)
+    page_size = (bfd_size_type) at_pagesz;
+
   while (total_size > 0)
     {
       if (size > total_size)
@@ -786,8 +792,7 @@ gcore_copy_callback (bfd *obfd, asection *osec)
 
 	  while (remaining > 0)
 	    {
-	      bfd_size_type chunk_size
-		= std::min (remaining, (bfd_size_type) FALLBACK_PAGE_SIZE);
+	      bfd_size_type chunk_size = std::min (remaining, page_size);
 
 	      if (target_read_memory (addr, p, chunk_size) != 0)
 		{
-- 
2.52.0