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From: Simon Marchi <simark@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] gdb/dwarf: fix UBsan crash in read_subrange_type Date: Fri, 20 Jan 2023 16:52:04 +0000 (GMT) [thread overview] Message-ID: <20230120165204.EE2F338582AC@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b70bff5ea52550c7cd48af7579a75ac2624ec13d commit b70bff5ea52550c7cd48af7579a75ac2624ec13d Author: Simon Marchi <simon.marchi@polymtl.ca> Date: Fri Jan 20 11:51:54 2023 -0500 gdb/dwarf: fix UBsan crash in read_subrange_type When running gdb.ada/arrayptr.exp (and others) on Ubuntu 22.04, with the `gnat-11` package installed (not `gnat`), with UBSan activated, I get: (gdb) break foo.adb:40 /home/smarchi/src/binutils-gdb/gdb/dwarf2/read.c:17689:20: runtime error: shift exponent 127 is too large for 64-bit type 'long unsigned int' The problematic DIEs are: 0x00001460: DW_TAG_subrange_type DW_AT_lower_bound [DW_FORM_data1] (0x00) DW_AT_upper_bound [DW_FORM_data16] (ffffffffffffffff3f00000000000000) DW_AT_name [DW_FORM_strp] ("foo__packed_array___XP7___XDLU_0__1180591620717411303423") DW_AT_type [DW_FORM_ref4] (0x0000153f "long_long_long_unsigned") DW_AT_GNAT_descriptive_type [DW_FORM_ref4] (0x0000147e) DW_AT_artificial [DW_FORM_flag_present] (true) 0x0000153f: DW_TAG_base_type DW_AT_byte_size [DW_FORM_data1] (0x10) DW_AT_encoding [DW_FORM_data1] (DW_ATE_unsigned) DW_AT_name [DW_FORM_strp] ("long_long_long_unsigned") DW_AT_artificial [DW_FORM_flag_present] (true) When processed by this code: negative_mask = -((ULONGEST) 1 << (base_type->length () * TARGET_CHAR_BIT - 1)); if (low.kind () == PROP_CONST && !base_type->is_unsigned () && (low.const_val () & negative_mask)) low.set_const_val (low.const_val () | negative_mask); When the base type's length (16 bytes in this case) is larger than a ULONGEST (typically 8 bytes), the bit shift is too large. My obvious fix is just to skip the fixup for base types larger than a ULONGEST (8 bytes). I don't think we really handle constant attribute values larger than 8 bytes anyway, so this is part of a much larger problem. Add a test that replicates this situation, but uses bounds that fit in a signed 64 bit, so we get a sensible result. Change-Id: I8d0a24f3edd83b44e0761a0ce38922d3e2e112fb Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29386 Diff: --- gdb/dwarf2/read.c | 29 +++++++++++++++++++---------- gdb/testsuite/gdb.dwarf2/subrange.exp | 22 ++++++++++++++++++++++ 2 files changed, 41 insertions(+), 10 deletions(-) diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index 44b54f77de9..cd937f24ee7 100644 --- a/gdb/dwarf2/read.c +++ b/gdb/dwarf2/read.c @@ -17588,7 +17588,6 @@ read_subrange_type (struct die_info *die, struct dwarf2_cu *cu) int low_default_is_valid; int high_bound_is_count = 0; const char *name; - ULONGEST negative_mask; orig_base_type = read_subrange_index_type (die, cu); @@ -17684,15 +17683,25 @@ read_subrange_type (struct die_info *die, struct dwarf2_cu *cu) with GCC, for instance, where the ambiguous DW_FORM_dataN form is used instead. To work around that ambiguity, we treat the bounds as signed, and thus sign-extend their values, when - the base type is signed. */ - negative_mask = - -((ULONGEST) 1 << (base_type->length () * TARGET_CHAR_BIT - 1)); - if (low.kind () == PROP_CONST - && !base_type->is_unsigned () && (low.const_val () & negative_mask)) - low.set_const_val (low.const_val () | negative_mask); - if (high.kind () == PROP_CONST - && !base_type->is_unsigned () && (high.const_val () & negative_mask)) - high.set_const_val (high.const_val () | negative_mask); + the base type is signed. + + Skip it if the base type's length is larger than ULONGEST, to avoid + the undefined behavior of a too large left shift. We don't really handle + constants larger than 8 bytes anyway, at the moment. */ + + if (base_type->length () <= sizeof (ULONGEST)) + { + ULONGEST negative_mask + = -((ULONGEST) 1 << (base_type->length () * TARGET_CHAR_BIT - 1)); + + if (low.kind () == PROP_CONST + && !base_type->is_unsigned () && (low.const_val () & negative_mask)) + low.set_const_val (low.const_val () | negative_mask); + + if (high.kind () == PROP_CONST + && !base_type->is_unsigned () && (high.const_val () & negative_mask)) + high.set_const_val (high.const_val () | negative_mask); + } /* Check for bit and byte strides. */ struct dynamic_prop byte_stride_prop; diff --git a/gdb/testsuite/gdb.dwarf2/subrange.exp b/gdb/testsuite/gdb.dwarf2/subrange.exp index 97743ee1099..4d7bcfb5f9c 100644 --- a/gdb/testsuite/gdb.dwarf2/subrange.exp +++ b/gdb/testsuite/gdb.dwarf2/subrange.exp @@ -77,6 +77,26 @@ Dwarf::assemble $asm_file { {name subrange_with_buggy_negative_bounds_variable} {type :$subrange_with_buggy_negative_bounds_label} } + + # This subrange's base type is 16-bytes long (although the bounds fit in + # signed 64-bit). This is to test the fix for PR 29386. + declare_labels a_16_byte_integer_label a_16_byte_subrange_label + + a_16_byte_integer_label: base_type { + {byte_size 16 udata} + {encoding @DW_ATE_signed} + } + + a_16_byte_subrange_label: subrange_type { + {lower_bound -9223372036854775808 DW_FORM_sdata} + {upper_bound 9223372036854775807 DW_FORM_sdata} + {type :$a_16_byte_integer_label} + } + + DW_TAG_variable { + {name a_16_byte_subrange_variable} + {type :$a_16_byte_subrange_label} + } } } } @@ -92,3 +112,5 @@ gdb_test "ptype TByteArray" \ "type = array \\\[0\\.\\.191\\\] of byte" gdb_test "ptype subrange_with_buggy_negative_bounds_variable" \ "type = -16\\.\\.-12" +gdb_test "ptype a_16_byte_subrange_variable" \ + "type = -9223372036854775808\\.\\.9223372036854775807"
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