[PATCH] Factor out the common code in lookup_{static,global}_symbol
Simon Marchi
simark@simark.ca
Sat Aug 3 23:41:00 GMT 2019
On 2019-08-02 9:04 p.m., Christian Biesinger via gdb-patches wrote:
> Thanks for the suggestion, that does seem better.
>
> The two functions are extremely similar; this factors out their code into
> a shared _internal function.
I am reasonably convinced that this is correct. lookup_static_symbol currently
iterates objfiles by simply iterating the linked list. Now it will use
gdbarch_iterate_over_objfiles_in_search_order, with current_objfile == NULL. The
only gdbarch that implements it is Windows (windows_iterate_over_objfiles_in_search_order)
and with current_objfile == NULL, it goes back to iterating the objfiles linked list directly.
So there shouldn't be any functional change.
> gdb/ChangeLog:
>
> 2019-08-02 Christian Biesinger <cbiesinger@google.com>
>
> * symtab.c (lookup_static_symbol): Call the new function (and move
> it down to be next to lookup_global_symbol).
> (struct global_sym_lookup_data): Add block_enum member.
> (lookup_symbol_global_iterator_cb): Pass block_index instead of
> GLOBAL_BLOCK to lookup_symbol_in_objfile.
> (lookup_global_symbol_internal): New function.
> (lookup_global_symbol): Call new function.
> ---
> gdb/symtab.c | 81 +++++++++++++++++++++++-----------------------------
> 1 file changed, 36 insertions(+), 45 deletions(-)
>
> diff --git a/gdb/symtab.c b/gdb/symtab.c
> index 87a0c8e4da..55df92f3e0 100644
> --- a/gdb/symtab.c
> +++ b/gdb/symtab.c
> @@ -2566,44 +2566,6 @@ lookup_symbol_in_objfile (struct objfile *objfile, enum block_enum block_index,
> return result;
> }
>
> -/* See symtab.h. */
> -
> -struct block_symbol
> -lookup_static_symbol (const char *name, const domain_enum domain)
> -{
> - struct symbol_cache *cache = get_symbol_cache (current_program_space);
> - struct block_symbol result;
> - struct block_symbol_cache *bsc;
> - struct symbol_cache_slot *slot;
> -
> - /* Lookup in STATIC_BLOCK is not current-objfile-dependent, so just pass
> - NULL for OBJFILE_CONTEXT. */
> - result = symbol_cache_lookup (cache, NULL, STATIC_BLOCK, name, domain,
> - &bsc, &slot);
> - if (result.symbol != NULL)
> - {
> - if (SYMBOL_LOOKUP_FAILED_P (result))
> - return {};
> - return result;
> - }
> -
> - for (objfile *objfile : current_program_space->objfiles ())
> - {
> - result = lookup_symbol_in_objfile (objfile, STATIC_BLOCK, name, domain);
> - if (result.symbol != NULL)
> - {
> - /* Still pass NULL for OBJFILE_CONTEXT here. */
> - symbol_cache_mark_found (bsc, slot, NULL, result.symbol,
> - result.block);
> - return result;
> - }
> - }
> -
> - /* Still pass NULL for OBJFILE_CONTEXT here. */
> - symbol_cache_mark_not_found (bsc, slot, NULL, name, domain);
> - return {};
> -}
> -
> /* Private data to be used with lookup_symbol_global_iterator_cb. */
>
> struct global_sym_lookup_data
> @@ -2614,6 +2576,9 @@ struct global_sym_lookup_data
> /* The domain to use for our search. */
> domain_enum domain;
>
> + /* The block index in which to search */
> + enum block_enum block_index;
> +
> /* The field where the callback should store the symbol if found.
> It should be initialized to {NULL, NULL} before the search is started. */
> struct block_symbol result;
> @@ -2634,7 +2599,7 @@ lookup_symbol_global_iterator_cb (struct objfile *objfile,
> gdb_assert (data->result.symbol == NULL
> && data->result.block == NULL);
>
> - data->result = lookup_symbol_in_objfile (objfile, GLOBAL_BLOCK,
> + data->result = lookup_symbol_in_objfile (objfile, data->block_index,
> data->name, data->domain);
>
> /* If we found a match, tell the iterator to stop. Otherwise,
> @@ -2642,12 +2607,14 @@ lookup_symbol_global_iterator_cb (struct objfile *objfile,
> return (data->result.symbol != NULL);
> }
>
> -/* See symtab.h. */
> -
> +/* This function contains the common code of lookup_{global,static}_symbol.
> + BLOCK is only used if BLOCK_INDEX is GLOBAL_SCOPE, in which case it is
> + used to retrieve the objfile to start the lookup in. */
> struct block_symbol
> -lookup_global_symbol (const char *name,
> - const struct block *block,
> - const domain_enum domain)
> +lookup_global_symbol_internal (const char *name,
> + enum block_enum block_index,
> + const struct block *block,
> + const domain_enum domain)
Make this function static. And to be pedant, add a newline between the doc and function name.
> {
> struct symbol_cache *cache = get_symbol_cache (current_program_space);
> struct block_symbol result;
> @@ -2656,11 +2623,14 @@ lookup_global_symbol (const char *name,
> struct block_symbol_cache *bsc;
> struct symbol_cache_slot *slot;
>
> + gdb_assert (block_index == GLOBAL_BLOCK || block_index == STATIC_BLOCK);
> + gdb_assert (block == nullptr || block_index == GLOBAL_BLOCK);
> +
> objfile = lookup_objfile_from_block (block);
>
> /* First see if we can find the symbol in the cache.
> This works because we use the current objfile to qualify the lookup. */
> - result = symbol_cache_lookup (cache, objfile, GLOBAL_BLOCK, name, domain,
> + result = symbol_cache_lookup (cache, objfile, block_index, name, domain,
> &bsc, &slot);
> if (result.symbol != NULL)
> {
> @@ -2678,6 +2648,7 @@ lookup_global_symbol (const char *name,
> {
> memset (&lookup_data, 0, sizeof (lookup_data));
> lookup_data.name = name;
> + lookup_data.block_index = block_index;
> lookup_data.domain = domain;
> gdbarch_iterate_over_objfiles_in_search_order
> (objfile != NULL ? get_objfile_arch (objfile) : target_gdbarch (),
> @@ -2693,6 +2664,26 @@ lookup_global_symbol (const char *name,
> return result;
> }
>
> +/* See symtab.h. */
> +
> +struct block_symbol
> +lookup_static_symbol (const char *name, const domain_enum domain)
> +{
> + /* TODO: Should static symbol lookup start with a block as well, so we can
> + prefer a static symbol in the current CU? */
That's a good question. So one of the things using lookup_static_symbol is the
gdb.lookup_static_symbol Python function you recently added. Right now, it is not
context sensitive. For example, here I have two files with each a static variable
`allo`, one with value 22 and the other with value 33:
(gdb) python print(gdb.lookup_static_symbol('allo').value())
22
(gdb) print allo
$1 = 22
(gdb) s
fonction () at test2.c:6
6 printf("allo = %d\n", allo);
(gdb) python print(gdb.lookup_static_symbol('allo').value())
22
(gdb) print allo
$2 = 33
As you can see, gdb.lookup_static_symbol will always find the same symbol,
regardless of the current context, unlike `print`, which ends up using lookup_symbol_aux.
Should functions like gdb.lookup_static_symbol implicitly prioritize the current context
(e.g. current CU)? I think something like that makes sense for the command line of GDB,
used interactively. But for an API, is it strange to get different results when calling
gdb.lookup_static_symbol with the same parameters at different times?
Simon
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