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* [binutils-gdb] [aarch64/arm] Properly extract the return value returned in memory
@ 2022-03-14 10:39 Luis Machado
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From: Luis Machado @ 2022-03-14 10:39 UTC (permalink / raw)
To: gdb-cvs
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=bab22d0640914384d467e09c3e796585fd08e7c6
commit bab22d0640914384d467e09c3e796585fd08e7c6
Author: Luis Machado <luis.machado@arm.com>
Date: Tue Jan 4 14:06:36 2022 -0300
[aarch64/arm] Properly extract the return value returned in memory
When running gdb.cp/non-trivial-retval.exp, the following shows up for
both aarch64-linux and armhf-linux:
Breakpoint 3, f1 (i1=23, i2=100) at src/gdb/testsuite/gdb.cp/non-trivial-retval.cc:35
35 A a;
(gdb) finish
Run till exit from #0 f1 (i1=23, i2=100) at src/gdb/testsuite/gdb.cp/non-trivial-retval.cc:35
main () at /src/gdb/testsuite/gdb.cp/non-trivial-retval.cc:163
163 B b = f2 (i1, i2);
Value returned is $6 = {a = -11952}
(gdb)
The return value should be {a = 123} instead. This happens because the
backends don't extract the return value from the correct location. GDB should
fetch a pointer to the memory location from X8 for aarch64 and r0 for armhf.
With the patch, gdb.cp/non-trivial-retval.exp has full passes on
aarch64-linux and armhf-linux on Ubuntu 20.04/18.04.
The problem only shows up with the "finish" command. The "call" command
works correctly and displays the correct return value.
This is also related to PR gdb/28681
(https://sourceware.org/bugzilla/show_bug.cgi?id=28681) and fixes FAIL's in
gdb.ada/mi_var_array.exp.
A new testcase is provided, and it exercises GDB's ability to "finish" a
function that returns a large struct (> 16 bytes) and display the
contents of this struct correctly. This has always been incorrect for
these backends, but no testcase exercised this particular scenario.
Diff:
---
gdb/aarch64-tdep.c | 21 ++++++++++--
gdb/arm-tdep.c | 32 ++++++++++++++++--
gdb/testsuite/gdb.base/retval-large-struct.c | 45 ++++++++++++++++++++++++++
gdb/testsuite/gdb.base/retval-large-struct.exp | 37 +++++++++++++++++++++
4 files changed, 130 insertions(+), 5 deletions(-)
diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index b3efb3ebaff..3f3a65240c0 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -2362,7 +2362,8 @@ aarch64_return_in_memory (struct gdbarch *gdbarch, struct type *type)
return 0;
}
- if (TYPE_LENGTH (type) > 16)
+ if (TYPE_LENGTH (type) > 16
+ || !language_pass_by_reference (type).trivially_copyable)
{
/* PCS B.6 Aggregates larger than 16 bytes are passed by
invisible reference. */
@@ -2474,8 +2475,24 @@ aarch64_return_value (struct gdbarch *gdbarch, struct value *func_value,
{
if (aarch64_return_in_memory (gdbarch, valtype))
{
+ /* From the AAPCS64's Result Return section:
+
+ "Otherwise, the caller shall reserve a block of memory of
+ sufficient size and alignment to hold the result. The address
+ of the memory block shall be passed as an additional argument to
+ the function in x8. */
+
aarch64_debug_printf ("return value in memory");
- return RETURN_VALUE_STRUCT_CONVENTION;
+
+ if (readbuf)
+ {
+ CORE_ADDR addr;
+
+ regcache->cooked_read (AARCH64_STRUCT_RETURN_REGNUM, &addr);
+ read_memory (addr, readbuf, TYPE_LENGTH (valtype));
+ }
+
+ return RETURN_VALUE_ABI_RETURNS_ADDRESS;
}
}
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index d36856e1f3b..8e245648f23 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -8075,7 +8075,8 @@ arm_return_in_memory (struct gdbarch *gdbarch, struct type *type)
{
/* The AAPCS says all aggregates not larger than a word are returned
in a register. */
- if (TYPE_LENGTH (type) <= ARM_INT_REGISTER_SIZE)
+ if (TYPE_LENGTH (type) <= ARM_INT_REGISTER_SIZE
+ && language_pass_by_reference (type).trivially_copyable)
return 0;
return 1;
@@ -8086,7 +8087,8 @@ arm_return_in_memory (struct gdbarch *gdbarch, struct type *type)
/* All aggregate types that won't fit in a register must be returned
in memory. */
- if (TYPE_LENGTH (type) > ARM_INT_REGISTER_SIZE)
+ if (TYPE_LENGTH (type) > ARM_INT_REGISTER_SIZE
+ || !language_pass_by_reference (type).trivially_copyable)
return 1;
/* In the ARM ABI, "integer" like aggregate types are returned in
@@ -8307,9 +8309,33 @@ arm_return_value (struct gdbarch *gdbarch, struct value *function,
|| valtype->code () == TYPE_CODE_UNION
|| valtype->code () == TYPE_CODE_ARRAY)
{
+ /* From the AAPCS document:
+
+ Result return:
+
+ A Composite Type larger than 4 bytes, or whose size cannot be
+ determined statically by both caller and callee, is stored in memory
+ at an address passed as an extra argument when the function was
+ called (Parameter Passing, rule A.4). The memory to be used for the
+ result may be modified at any point during the function call.
+
+ Parameter Passing:
+
+ A.4: If the subroutine is a function that returns a result in memory,
+ then the address for the result is placed in r0 and the NCRN is set
+ to r1. */
if (tdep->struct_return == pcc_struct_return
|| arm_return_in_memory (gdbarch, valtype))
- return RETURN_VALUE_STRUCT_CONVENTION;
+ {
+ if (readbuf)
+ {
+ CORE_ADDR addr;
+
+ regcache->cooked_read (ARM_A1_REGNUM, &addr);
+ read_memory (addr, readbuf, TYPE_LENGTH (valtype));
+ }
+ return RETURN_VALUE_ABI_RETURNS_ADDRESS;
+ }
}
else if (valtype->code () == TYPE_CODE_COMPLEX)
{
diff --git a/gdb/testsuite/gdb.base/retval-large-struct.c b/gdb/testsuite/gdb.base/retval-large-struct.c
new file mode 100644
index 00000000000..ae459741220
--- /dev/null
+++ b/gdb/testsuite/gdb.base/retval-large-struct.c
@@ -0,0 +1,45 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2022 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+struct big_struct_t
+{
+ int int_array[5];
+ double double_array[5];
+ char char_array[5];
+};
+
+struct big_struct_t big_struct =
+{
+ {1, 2, 3, 4, 5},
+ {3.25, 5.0, 6.25, 1.325, -1.95},
+ "abcde"
+};
+
+struct big_struct_t return_large_struct (void)
+{
+ return big_struct;
+}
+
+int
+main (int argc, char **argv)
+{
+ struct big_struct_t test_struct;
+
+ test_struct = return_large_struct ();
+
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.base/retval-large-struct.exp b/gdb/testsuite/gdb.base/retval-large-struct.exp
new file mode 100644
index 00000000000..11bc4d5fbdf
--- /dev/null
+++ b/gdb/testsuite/gdb.base/retval-large-struct.exp
@@ -0,0 +1,37 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the gdb testsuite
+#
+# Test if "finish" behaves correctly when a function returns a
+# large (> 16 bytes) struct.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
+ return -1
+}
+
+if {![runto_main]} {
+ return -1
+}
+
+set pattern ".* = \\{int_array = \\{1, 2, 3, 4, 5\\}, double_array = \\{3.25, 5, 6.25, 1.325, -1.95\\}, char_array = \"abcde\"\\}"
+
+gdb_test "p return_large_struct ()" $pattern
+
+gdb_breakpoint "return_large_struct"
+gdb_continue_to_breakpoint "Break in print_large_struct"
+gdb_test "finish" $pattern "finish from return_large_struct"
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2022-03-14 10:39 [binutils-gdb] [aarch64/arm] Properly extract the return value returned in memory Luis Machado
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