* [PATCH] Fix casting in-memory values of primitive types to const reference [not found] <20240320160844.106-1-ssbssa.ref@yahoo.de> @ 2024-03-20 16:08 ` Hannes Domani 2024-03-20 17:05 ` Tom Tromey 0 siblings, 1 reply; 4+ messages in thread From: Hannes Domani @ 2024-03-20 16:08 UTC (permalink / raw) To: gdb-patches It's currently not possible to cast an in-memory value of a primitive type to const reference: ``` (gdb) p Q.id $1 = 42 (gdb) p (int&)Q.id $2 = (int &) @0x22fd0c: 42 (gdb) p (const int&)Q.id Attempt to take address of value not located in memory. ``` And if in a function call an argument needs the same kind of casting, it also doesn't work: ``` (gdb) l f3 39 int f3(const int &i) 40 { 41 return i; 42 } (gdb) p f3(Q.id) Attempt to take address of value not located in memory. ``` It's because when the constness of the type changes in a call to value_cast, a new not_lval value is allocated, which doesn't exist in the target memory. Fixed by ignoring const/volatile/restrict qualifications in value_cast when comparing cast type to original type, so the new value will point to the same location as the original value: ``` (gdb) p (int&)i $2 = (int &) @0x39f72c: 1 (gdb) p (const int&)i $3 = (const int &) @0x39f72c: 1 (gdb) p f3(Q.id) $4 = 42 ``` Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=19423 --- gdb/testsuite/gdb.cp/casts.exp | 3 +++ gdb/testsuite/gdb.cp/ref-params.cc | 6 ++++++ gdb/testsuite/gdb.cp/ref-params.exp | 1 + gdb/valops.c | 3 ++- 4 files changed, 12 insertions(+), 1 deletion(-) diff --git a/gdb/testsuite/gdb.cp/casts.exp b/gdb/testsuite/gdb.cp/casts.exp index ca82ab084b9..9f7638c8aee 100644 --- a/gdb/testsuite/gdb.cp/casts.exp +++ b/gdb/testsuite/gdb.cp/casts.exp @@ -180,6 +180,9 @@ gdb_test "print (unsigned long long) (LeftRight *) (Right *) &gd == gd_value" \ gdb_test "print (unsigned long long) (LeftRight *) (Right *) r_value == gd_value" \ " = true" +gdb_test "print (const int &) gd.left" \ + " = \\(const int \\&\\) @$nonzero_hex: 23" + gdb_test "print reinterpret_cast<LeftRight *>(l) == lr_l" " = true" gdb_test "print reinterpret_cast<LeftRight *>(r) == lr_r" " = true" gdb_test "print reinterpret_cast<Left *>(lr) == l_lr" " = true" diff --git a/gdb/testsuite/gdb.cp/ref-params.cc b/gdb/testsuite/gdb.cp/ref-params.cc index f038d71fe10..3ef28688607 100644 --- a/gdb/testsuite/gdb.cp/ref-params.cc +++ b/gdb/testsuite/gdb.cp/ref-params.cc @@ -36,6 +36,11 @@ int f2(Child& C) return f1(C); /* Set breakpoint marker2 here. */ } +int f3(const int &i) +{ + return i; +} + struct OtherParent { OtherParent (int other_id0) : other_id(other_id0) { } int other_id; @@ -64,6 +69,7 @@ int main(void) f2(Q); f2(QR); + f3(Q.id); MultiChild MQ(53); MultiChild& MQR = MQ; diff --git a/gdb/testsuite/gdb.cp/ref-params.exp b/gdb/testsuite/gdb.cp/ref-params.exp index 03bb8e62496..e5c28e6e2ad 100644 --- a/gdb/testsuite/gdb.cp/ref-params.exp +++ b/gdb/testsuite/gdb.cp/ref-params.exp @@ -62,3 +62,4 @@ gdb_test "print mf2(MQ)" ".* = 106" gdb_test "print f1(MQR)" ".* = 53" gdb_test "print mf1(MQR)" ".* = 106" gdb_test "print mf2(MQR)" ".* = 106" +gdb_test "print f3(Q.id)" ".* = 42" diff --git a/gdb/valops.c b/gdb/valops.c index 0a4e57672ce..14c12142112 100644 --- a/gdb/valops.c +++ b/gdb/valops.c @@ -411,7 +411,8 @@ value_cast (struct type *type, struct value *arg2) In this case we want to preserve the LVAL of ARG2 as this allows the resulting value to be used in more places. We do this by calling VALUE_COPY if appropriate. */ - if (types_deeply_equal (arg2->type (), type)) + if (types_deeply_equal (make_unqualified_type (arg2->type ()), + make_unqualified_type (type))) { /* If the types are exactly equal then we can avoid creating a new value completely. */ -- 2.35.1 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix casting in-memory values of primitive types to const reference 2024-03-20 16:08 ` [PATCH] Fix casting in-memory values of primitive types to const reference Hannes Domani @ 2024-03-20 17:05 ` Tom Tromey 2024-03-20 17:25 ` Hannes Domani 0 siblings, 1 reply; 4+ messages in thread From: Tom Tromey @ 2024-03-20 17:05 UTC (permalink / raw) To: Hannes Domani; +Cc: gdb-patches >>>>> "Hannes" == Hannes Domani <ssbssa@yahoo.de> writes: Hannes> It's currently not possible to cast an in-memory value of a primitive Hannes> type to const reference: Thank you for the patch. I think it is ok. However I suspect there may be other bugs here. Approved-By: Tom Tromey <tom@tromey.com> Hannes> Fixed by ignoring const/volatile/restrict qualifications in Hannes> value_cast when comparing cast type to original type, so the new Hannes> value will point to the same location as the original value: Hannes> - if (types_deeply_equal (arg2->type (), type)) Hannes> + if (types_deeply_equal (make_unqualified_type (arg2->type ()), Hannes> + make_unqualified_type (type))) This code seems slightly weird in that it isn't calling check_typedef. So, I wonder what happens if typedefs are involved, for example if you did: typedef const int ci; (gdb) print (ci&) Q.id thanks, Tom ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix casting in-memory values of primitive types to const reference 2024-03-20 17:05 ` Tom Tromey @ 2024-03-20 17:25 ` Hannes Domani 2024-03-20 17:33 ` Tom Tromey 0 siblings, 1 reply; 4+ messages in thread From: Hannes Domani @ 2024-03-20 17:25 UTC (permalink / raw) To: Tom Tromey; +Cc: gdb-patches Am Mittwoch, 20. März 2024 um 18:05:48 MEZ hat Tom Tromey <tom@tromey.com> Folgendes geschrieben: > >>>>> "Hannes" == Hannes Domani <ssbssa@yahoo.de> writes: > > Hannes> It's currently not possible to cast an in-memory value of a primitive > Hannes> type to const reference: > > Thank you for the patch. > > I think it is ok. However I suspect there may be other bugs here. > > Approved-By: Tom Tromey <tom@tromey.com> Pushed, thanks. > Hannes> Fixed by ignoring const/volatile/restrict qualifications in > Hannes> value_cast when comparing cast type to original type, so the new > Hannes> value will point to the same location as the original value: > > Hannes> - if (types_deeply_equal (arg2->type (), type)) > Hannes> + if (types_deeply_equal (make_unqualified_type (arg2->type ()), > Hannes> + make_unqualified_type (type))) > > This code seems slightly weird in that it isn't calling check_typedef. > So, I wonder what happens if typedefs are involved, for example if you > did: > > typedef const int ci; > > (gdb) print (ci&) Q.id This happens: (gdb) p (ci&) Q.id $1 = (const int &) @0x3cfb8c: 42 Because check_typedef is called when the reference is removed: ``` /* Check if we are casting struct reference to struct reference. */ if (TYPE_IS_REFERENCE (check_typedef (type))) { /* We dereference type; then we recurse and finally we generate value of the given reference. Nothing wrong with that. */ struct type *t1 = check_typedef (type); struct type *dereftype = check_typedef (t1->target_type ()); struct value *val = value_cast (dereftype, arg2); return value_ref (val, t1->code ()); } ``` Hannes ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix casting in-memory values of primitive types to const reference 2024-03-20 17:25 ` Hannes Domani @ 2024-03-20 17:33 ` Tom Tromey 0 siblings, 0 replies; 4+ messages in thread From: Tom Tromey @ 2024-03-20 17:33 UTC (permalink / raw) To: Hannes Domani; +Cc: Tom Tromey, gdb-patches >>>>> "Hannes" == Hannes Domani <ssbssa@yahoo.de> writes: Hannes> This happens: Hannes> (gdb) p (ci&) Q.id Hannes> $1 = (const int &) @0x3cfb8c: 42 Hannes> Because check_typedef is called when the reference is removed: Thanks for looking. Tom ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2024-03-20 17:42 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <20240320160844.106-1-ssbssa.ref@yahoo.de> 2024-03-20 16:08 ` [PATCH] Fix casting in-memory values of primitive types to const reference Hannes Domani 2024-03-20 17:05 ` Tom Tromey 2024-03-20 17:25 ` Hannes Domani 2024-03-20 17:33 ` Tom Tromey
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