From 8d7bcccb82d9a7efccd75d9552d007c62031e855 Mon Sep 17 00:00:00 2001 From: Tom Tromey Date: Thu, 10 May 2018 16:23:57 -0600 Subject: [PATCH] Move psymtabs to their own obstack Previously, the psymtab obstack was just a pointer to the objfile obstack. This patch changes psymtabs to use their own obstack, instead. A gdb::optional is used to avoid unnecessary allocation when the obstack is not needed. After this patch, the psymtab code lifetime model is that, in the core psymtab code, objects allocated on the psymtab obstack may point to other such objects, or to objects on the per-BFD obstack -- but never to the objfile obstack. Note however that this invariant is only obeyed the core psymtab code, and even there not quite fully: there is still a link from the psymtab to the full symtab. Symbol readers are free to work however they like; and in particular, even after this patch, in practice all symbol readers violate this invariant via the read_symtab_private field. gdb/ChangeLog 2019-01-10 Tom Tromey * objfiles.h (objfile::reset_psymtabs): Update. * objfiles.c (objfile::objfile): Update. * psymtab.h (psymtab_storage::obstack): Update. (psymtab_storage::m_obstack): Use gdb::optional. (class psymtab_storage): Update comment. Remove objfile parameter. * psymtab.c (psymtab_storage::psymtab_storage): Update. --- gdb/ChangeLog | 10 ++++++++++ gdb/objfiles.c | 2 +- gdb/objfiles.h | 2 +- gdb/psymtab.c | 5 ++--- gdb/psymtab.h | 26 +++++++++++++++++++++----- 5 files changed, 35 insertions(+), 10 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 4eeea5c12fb..32fe0bbe814 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,13 @@ +2019-01-10 Tom Tromey + + * objfiles.h (objfile::reset_psymtabs): Update. + * objfiles.c (objfile::objfile): Update. + * psymtab.h (psymtab_storage::obstack): Update. + (psymtab_storage::m_obstack): Use gdb::optional. + (class psymtab_storage): Update comment. Remove objfile + parameter. + * psymtab.c (psymtab_storage::psymtab_storage): Update. + 2019-01-10 Tom Tromey * psymtab.h (psymtab_storage::allocate_psymtab): New method. diff --git a/gdb/objfiles.c b/gdb/objfiles.c index 34154482124..255a3d636d1 100644 --- a/gdb/objfiles.c +++ b/gdb/objfiles.c @@ -369,7 +369,7 @@ build_objfile_section_table (struct objfile *objfile) objfile::objfile (bfd *abfd, const char *name, objfile_flags flags_) : flags (flags_), pspace (current_program_space), - partial_symtabs (new psymtab_storage (this)), + partial_symtabs (new psymtab_storage ()), obfd (abfd) { const char *expanded_name; diff --git a/gdb/objfiles.h b/gdb/objfiles.h index cde025d9d91..f7d08c43b3b 100644 --- a/gdb/objfiles.h +++ b/gdb/objfiles.h @@ -298,7 +298,7 @@ struct objfile void reset_psymtabs () { psymbol_map.clear (); - partial_symtabs.reset (new psymtab_storage (this)); + partial_symtabs.reset (new psymtab_storage ()); } diff --git a/gdb/psymtab.c b/gdb/psymtab.c index 7ead0eb81ad..e034fda3402 100644 --- a/gdb/psymtab.c +++ b/gdb/psymtab.c @@ -67,9 +67,8 @@ static struct compunit_symtab *psymtab_to_symtab (struct objfile *objfile, -psymtab_storage::psymtab_storage (struct objfile *objfile) - : psymbol_cache (psymbol_bcache_init ()), - m_obstack (&objfile->objfile_obstack) +psymtab_storage::psymtab_storage () + : psymbol_cache (psymbol_bcache_init ()) { } diff --git a/gdb/psymtab.h b/gdb/psymtab.h index a21e88fd0a0..26aeb29646e 100644 --- a/gdb/psymtab.h +++ b/gdb/psymtab.h @@ -31,13 +31,26 @@ struct partial_symbol; struct psymbol_bcache; /* An instance of this class manages the partial symbol tables and - partial symbols for a given objfile. */ + partial symbols for a given objfile. + + The core psymtab functions -- those in psymtab.c -- arrange for + nearly all psymtab- and psymbol-related allocations to happen + either in the psymtab_storage object (either on its obstack or in + other memory managed by this class), or on the per-BFD object. The + only link from the psymtab storage object back to the objfile (or + objfile_obstack) that is made by the core psymtab code is the + compunit_symtab member in the psymtab. + + However, it is up to each symbol reader to maintain this invariant + in other ways, if it wants to reuse psymtabs across multiple + objfiles. The main issue here is ensuring that read_symtab_private + does not point into objfile_obstack. */ class psymtab_storage { public: - explicit psymtab_storage (struct objfile *objfile); + psymtab_storage (); ~psymtab_storage (); @@ -60,7 +73,9 @@ public: struct obstack *obstack () { - return m_obstack; + if (!m_obstack.has_value ()) + m_obstack.emplace (); + return &*m_obstack; } /* Allocate storage for the "dependencies" field of a psymtab. @@ -108,9 +123,10 @@ private: struct partial_symtab *free_psymtabs = nullptr; - /* The obstack where allocations are made. */ + /* The obstack where allocations are made. This is lazily allocated + so that we don't waste memory when there are no psymtabs. */ - struct obstack *m_obstack; + gdb::optional m_obstack; }; -- 2.30.2