From 0e26741636bee18321d6743ecee6ae9effd35d1f Mon Sep 17 00:00:00 2001 From: Andrew Burgess Date: Thu, 16 Jul 2020 17:48:12 +0100 Subject: [PATCH] gdb/riscv: delete target descriptions when gdb exits MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit It was pointed out on IRC that the RISC-V target allocates target descriptions and stores them in a global map, and doesn't delete these target descriptions when GDB shuts down. This isn't a particular problem, the total number of target descriptions we can create is very limited so creating these on demand and holding them for the entire run on GDB seems reasonable. However, not deleting these objects on GDB exit means extra warnings are printed from tools like valgrind, and the address sanitiser, making it harder to spot real issues. As it's reasonably easy to have GDB correctly delete these objects on exit, lets just do that. I started by noticing that we already have a target_desc_up type, a wrapper around unique_ptr that calls a function that will correctly delete target descriptions, so I want to use that, but.... ...that type is declared in gdb/target-descriptions.h. If I try to include that file in gdb/arch/riscv.c I run into a problem, that file is compiled into both GDB and GDBServer. OK, I could guard the include with #ifdef, but surely we can do better. So then I decided to move the target_desc_up type into gdbsupport/tdesc.h, this is the interface file for generic code shared between GDB and GDBserver (relating to target descriptions). The actual implementation for the delete function still lives in gdb/target-description.c, but now gdb/arch/riscv.c can see the declaration. Problem solved.... ... but, though RISC-V doesn't use it I've now exposed the target_desc_up type to gdbserver, so in future someone _might_ start using it, which is fine, except right now there's no definition of the delete function - remember the delete I used is only defined in GDB code. No problem, I add an implementation of the delete operator into gdbserver/tdesc.cc, and all is good..... except.... I start getting this error from GCC: tdesc.cc:109:10: error: deleting object of polymorphic class type ‘target_desc’ which has non-virtual destructor might cause undefined behavior [-Werror=delete-non-virtual-dtor] Which is caused because gdbserver's target_desc type inherits from tdesc_element which has a virtual method, and so GCC worries that target_desc might be used as a base class. The solution is to declare gdbserver's target_desc class as final. This is fine so long as we never intent to inherit from target_desc (in gdbserver). But if we did then we'd want to make target_desc's destructor virtual anyway, so the error above would be resolved, and there wouldn't be an issue. gdb/ChangeLog: * arch/riscv.c (riscv_tdesc_cache): Change map type. (riscv_lookup_target_description): Return pointer out of unique_ptr. * target-descriptions.c (allocate_target_description): Add comment. (target_desc_deleter::operator()): Likewise. * target-descriptions.h (struct target_desc_deleter): Moved to gdbsupport/tdesc.h. (target_desc_up): Likewise. gdbserver/ChangeLog: * tdesc.cc (allocate_target_description): Add header comment. (target_desc_deleter::operator()): New function. * tdesc.h (struct target_desc): Declare as final. gdbsupport/ChangeLog: * tdesc.h (struct target_desc_deleter): Moved here from gdb/target-descriptions.h, extend comment. (target_desc_up): Likewise. --- gdb/ChangeLog | 12 ++++++++++++ gdb/arch/riscv.c | 8 +++++--- gdb/target-descriptions.c | 4 ++++ gdb/target-descriptions.h | 12 ------------ gdbserver/ChangeLog | 6 ++++++ gdbserver/tdesc.cc | 10 ++++++++++ gdbserver/tdesc.h | 2 +- gdbsupport/ChangeLog | 6 ++++++ gdbsupport/tdesc.h | 14 ++++++++++++++ 9 files changed, 58 insertions(+), 16 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 1b5bc8b458a..5a01458a46a 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,15 @@ +2020-07-17 Andrew Burgess + + * arch/riscv.c (riscv_tdesc_cache): Change map type. + (riscv_lookup_target_description): Return pointer out of + unique_ptr. + * target-descriptions.c (allocate_target_description): Add + comment. + (target_desc_deleter::operator()): Likewise. + * target-descriptions.h (struct target_desc_deleter): Moved to + gdbsupport/tdesc.h. + (target_desc_up): Likewise. + 2020-07-17 Tom Tromey * linux-nat.c (linux_nat_target::supports_non_stop) diff --git a/gdb/arch/riscv.c b/gdb/arch/riscv.c index a02c18b4c91..e43aafc1c2f 100644 --- a/gdb/arch/riscv.c +++ b/gdb/arch/riscv.c @@ -91,7 +91,7 @@ struct riscv_gdbarch_features_hasher /* Cache of previously seen target descriptions, indexed by the feature set that created them. */ static std::unordered_map riscv_tdesc_cache; /* See arch/riscv.h. */ @@ -99,10 +99,12 @@ static std::unordered_mapsecond; + return it->second.get (); target_desc *tdesc = riscv_create_target_description (features); diff --git a/gdb/target-descriptions.c b/gdb/target-descriptions.c index 2f4b17727b8..20d624c0c65 100644 --- a/gdb/target-descriptions.c +++ b/gdb/target-descriptions.c @@ -1206,12 +1206,16 @@ tdesc_create_feature (struct target_desc *tdesc, const char *name) return new_feature; } +/* See gdbsupport/tdesc.h. */ + struct target_desc * allocate_target_description (void) { return new target_desc (); } +/* See gdbsupport/tdesc.h. */ + void target_desc_deleter::operator() (struct target_desc *target_desc) const { diff --git a/gdb/target-descriptions.h b/gdb/target-descriptions.h index 6d842bf07ed..66a2c213dc2 100644 --- a/gdb/target-descriptions.h +++ b/gdb/target-descriptions.h @@ -225,18 +225,6 @@ struct type *tdesc_find_type (struct gdbarch *gdbarch, const char *id); int tdesc_register_in_reggroup_p (struct gdbarch *gdbarch, int regno, struct reggroup *reggroup); - -/* A deleter adapter for a target desc. */ - -struct target_desc_deleter -{ - void operator() (struct target_desc *desc) const; -}; - -/* A unique pointer specialization that holds a target_desc. */ - -typedef std::unique_ptr target_desc_up; - /* Methods for constructing a target description. */ void set_tdesc_architecture (struct target_desc *, diff --git a/gdbserver/ChangeLog b/gdbserver/ChangeLog index 1ee716f52d7..9d615870d17 100644 --- a/gdbserver/ChangeLog +++ b/gdbserver/ChangeLog @@ -1,3 +1,9 @@ +2020-07-17 Andrew Burgess + + * tdesc.cc (allocate_target_description): Add header comment. + (target_desc_deleter::operator()): New function. + * tdesc.h (struct target_desc): Declare as final. + 2020-07-13 Simon Marchi * server.cc (handle_query): Use std::vector of diff --git a/gdbserver/tdesc.cc b/gdbserver/tdesc.cc index d21688b932b..e639017cc31 100644 --- a/gdbserver/tdesc.cc +++ b/gdbserver/tdesc.cc @@ -93,12 +93,22 @@ init_target_desc (struct target_desc *tdesc, #endif } +/* See gdbsupport/tdesc.h. */ + struct target_desc * allocate_target_description (void) { return new target_desc (); } +/* See gdbsupport/tdesc.h. */ + +void +target_desc_deleter::operator() (struct target_desc *target_desc) const +{ + delete target_desc; +} + #ifndef IN_PROCESS_AGENT static const struct target_desc default_description {}; diff --git a/gdbserver/tdesc.h b/gdbserver/tdesc.h index f9ca478ff6d..681de64d0aa 100644 --- a/gdbserver/tdesc.h +++ b/gdbserver/tdesc.h @@ -27,7 +27,7 @@ /* A target description. Inherit from tdesc_feature so that target_desc can be used as tdesc_feature. */ -struct target_desc : tdesc_element +struct target_desc final : tdesc_element { /* A vector of elements of register definitions that describe the inferior's register set. */ diff --git a/gdbsupport/ChangeLog b/gdbsupport/ChangeLog index e1b040d5827..6b555cb9704 100644 --- a/gdbsupport/ChangeLog +++ b/gdbsupport/ChangeLog @@ -1,3 +1,9 @@ +2020-07-17 Andrew Burgess + + * tdesc.h (struct target_desc_deleter): Moved here + from gdb/target-descriptions.h, extend comment. + (target_desc_up): Likewise. + 2020-06-30 Tom Tromey PR build/26183: diff --git a/gdbsupport/tdesc.h b/gdbsupport/tdesc.h index 456e8e070b1..fdc2a6a3708 100644 --- a/gdbsupport/tdesc.h +++ b/gdbsupport/tdesc.h @@ -312,6 +312,20 @@ struct tdesc_feature : tdesc_element typedef std::unique_ptr tdesc_feature_up; +/* A deleter adapter for a target_desc. There are different + implementations of this deleter class in gdb and gdbserver because even + though the target_desc name is shared between the two projects, the + actual implementations of target_desc are completely different. */ + +struct target_desc_deleter +{ + void operator() (struct target_desc *desc) const; +}; + +/* A unique pointer specialization that holds a target_desc. */ + +typedef std::unique_ptr target_desc_up; + /* Allocate a new target_desc. */ target_desc *allocate_target_description (void); -- 2.30.2