Consider -fanalyzer on:
#include <stdint.h>
int32_t arr[10];
void int_arr_write_element_after_end_off_by_one(int32_t x)
{
arr[10] = x;
}
Trunk x86_64: https://godbolt.org/z/17zn3qYY4
Currently we emit:
<source>: In function 'int_arr_write_element_after_end_off_by_one':
<source>:7:11: warning: buffer overflow [CWE-787] [-Wanalyzer-out-of-bounds]
7 | arr[10] = x;
| ~~~~~~~~^~~
event 1
|
| 3 | int32_t arr[10];
| | ^~~
| | |
| | (1) capacity is 40 bytes
|
+--> 'int_arr_write_element_after_end_off_by_one': events 2-3
|
| 5 | void int_arr_write_element_after_end_off_by_one(int32_t x)
| | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| | |
| | (2) entry to 'int_arr_write_element_after_end_off_by_one'
| 6 | {
| 7 | arr[10] = x;
| | ~~~~~~~~~~~
| | |
| | (3) out-of-bounds write from byte 40 till byte 43 but 'arr' ends at byte 40
|
<source>:7:11: note: write of 4 bytes to beyond the end of 'arr'
7 | arr[10] = x;
| ~~~~~~~~^~~
This is worded in terms of bytes, due to the way -Wanalyzer-out-of-bounds
is implemented, but this isn't what the user wrote.
This patch tries to get closer to the user's code by adding a note about
array bounds when we're referring to an array. In the above example it
adds this trailing note:
note: valid subscripts for 'arr' are '[0]' to '[9]'
Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
Pushed to trunk as r13-4427-g7c655699ed51b0.
gcc/analyzer/ChangeLog:
PR analyzer/106626
* bounds-checking.cc (out_of_bounds::maybe_describe_array_bounds):
New.
(buffer_overflow::emit): Call maybe_describe_array_bounds.
(buffer_overread::emit): Likewise.
(buffer_underflow::emit): Likewise.
(buffer_underread::emit): Likewise.
gcc/testsuite/ChangeLog:
PR analyzer/106626
* gcc.dg/analyzer/call-summaries-2.c: Add dg-message for expected
note about valid indexes.
* gcc.dg/analyzer/out-of-bounds-1.c: Likewise, fixing up existing
dg-message directives.
* gcc.dg/analyzer/out-of-bounds-write-char-arr.c: Likewise.
* gcc.dg/analyzer/out-of-bounds-write-int-arr.c: Likewise.
Signed-off-by: David Malcolm <dmalcolm@redhat.com>
---
gcc/analyzer/bounds-checking.cc | 46 +++++++++++++++++--
.../gcc.dg/analyzer/call-summaries-2.c | 1 +
.../gcc.dg/analyzer/out-of-bounds-1.c | 16 ++++---
.../analyzer/out-of-bounds-write-char-arr.c | 6 +++
.../analyzer/out-of-bounds-write-int-arr.c | 6 +++
5 files changed, 64 insertions(+), 11 deletions(-)
@@ -71,6 +71,34 @@ public:
}
protected:
+ /* Potentially add a note about valid ways to index this array, such
+ as (given "int arr[10];"):
+ note: valid subscripts for 'arr' are '[0]' to '[9]'
+ We print the '[' and ']' characters so as to express the valid
+ subscripts using C syntax, rather than just as byte ranges,
+ which hopefully is more clear to the user. */
+ void
+ maybe_describe_array_bounds (location_t loc) const
+ {
+ if (!m_diag_arg)
+ return;
+ tree t = TREE_TYPE (m_diag_arg);
+ if (!t)
+ return;
+ if (TREE_CODE (t) != ARRAY_TYPE)
+ return;
+ tree domain = TYPE_DOMAIN (t);
+ if (!domain)
+ return;
+ tree max_idx = TYPE_MAX_VALUE (domain);
+ if (!max_idx)
+ return;
+ tree min_idx = TYPE_MIN_VALUE (domain);
+ inform (loc,
+ "valid subscripts for %qE are %<[%E]%> to %<[%E]%>",
+ m_diag_arg, min_idx, max_idx);
+ }
+
const region *m_reg;
tree m_diag_arg;
byte_range m_out_of_bounds_range;
@@ -165,6 +193,8 @@ public:
inform (rich_loc->get_loc (),
"write to beyond the end of %qE",
m_diag_arg);
+
+ maybe_describe_array_bounds (rich_loc->get_loc ());
}
return warned;
@@ -245,6 +275,8 @@ public:
inform (rich_loc->get_loc (),
"read from after the end of %qE",
m_diag_arg);
+
+ maybe_describe_array_bounds (rich_loc->get_loc ());
}
return warned;
@@ -297,8 +329,11 @@ public:
{
diagnostic_metadata m;
m.add_cwe (124);
- return warning_meta (rich_loc, m, get_controlling_option (),
- "buffer underflow");
+ bool warned = warning_meta (rich_loc, m, get_controlling_option (),
+ "buffer underflow");
+ if (warned)
+ maybe_describe_array_bounds (rich_loc->get_loc ());
+ return warned;
}
label_text describe_final_event (const evdesc::final_event &ev)
@@ -346,8 +381,11 @@ public:
{
diagnostic_metadata m;
m.add_cwe (127);
- return warning_meta (rich_loc, m, get_controlling_option (),
- "buffer underread");
+ bool warned = warning_meta (rich_loc, m, get_controlling_option (),
+ "buffer underread");
+ if (warned)
+ maybe_describe_array_bounds (rich_loc->get_loc ());
+ return warned;
}
label_text describe_final_event (const evdesc::final_event &ev)
@@ -330,6 +330,7 @@ int test_returns_element_ptr (int j)
__analyzer_eval (*returns_element_ptr (1) == 8); /* { dg-warning "TRUE" } */
__analyzer_eval (*returns_element_ptr (2) == 9); /* { dg-warning "TRUE" } */
return *returns_element_ptr (3); /* { dg-warning "buffer overread" } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[2\\\]'" "valid subscript note" { target *-*-* } .-1 } */
}
int returns_offset (int arr[3], int i)
@@ -25,8 +25,9 @@ void test1 (void)
id_sequence[2] = 345;
id_sequence[3] = 456; /* { dg-line test1 } */
- /* { dg-warning "overflow" "warning" { target *-*-* } test1 } */
- /* { dg-message "" "note" { target *-*-* } test1 } */
+ /* { dg-warning "stack-based buffer overflow" "warning" { target *-*-* } test1 } */
+ /* { dg-message "write of 4 bytes to beyond the end of 'id_sequence'" "num bad bytes note" { target *-*-* } test1 } */
+ /* { dg-message "valid subscripts for 'id_sequence' are '\\\[0\\\]' to '\\\[2\\\]'" "valid subscript note" { target *-*-* } test1 } */
}
void test2 (void)
@@ -46,8 +47,9 @@ void test3 (void)
for (int i = n; i >= 0; i--)
arr[i] = i; /* { dg-line test3 } */
- /* { dg-warning "overflow" "warning" { target *-*-* } test3 } */
- /* { dg-message "" "note" { target *-*-* } test3 } */
+ /* { dg-warning "stack-based buffer overflow" "warning" { target *-*-* } test3 } */
+ /* { dg-message "write of 4 bytes to beyond the end of 'arr'" "num bad bytes note" { target *-*-* } test3 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[3\\\]'" "valid subscript note" { target *-*-* } test3 } */
}
void test4 (void)
@@ -72,7 +74,7 @@ void test5 (void)
*last_el = 4; /* { dg-line test5 } */
free (arr);
- /* { dg-warning "overflow" "warning" { target *-*-* } test5 } */
+ /* { dg-warning "heap-based buffer overflow" "warning" { target *-*-* } test5 } */
/* { dg-message "" "note" { target *-*-* } test5 } */
}
@@ -89,9 +91,9 @@ void test6 (void)
printf ("x=%d y=%d *p=%d *q=%d\n" , x, y, *p, *q); /* { dg-line test6c } */
}
- /* { dg-warning "overflow" "warning" { target *-*-* } test6b } */
+ /* { dg-warning "buffer overflow" "warning" { target *-*-* } test6b } */
/* { dg-message "" "note" { target *-*-* } test6b } */
- /* { dg-warning "overread" "warning" { target *-*-* } test6c } */
+ /* { dg-warning "buffer overread" "warning" { target *-*-* } test6c } */
/* { dg-message "" "note" { target *-*-* } test6c } */
}
@@ -4,18 +4,21 @@ void int_arr_write_element_before_start_far(char x)
{
arr[-100] = x; /* { dg-warning "buffer underflow" "warning" } */
/* { dg-message "out-of-bounds write at byte -100 but 'arr' starts at byte 0" "final event" { target *-*-* } .-1 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-2 } */
}
void int_arr_write_element_before_start_near(char x)
{
arr[-2] = x; /* { dg-warning "buffer underflow" "warning" } */
/* { dg-message "out-of-bounds write at byte -2 but 'arr' starts at byte 0" "final event" { target *-*-* } .-1 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-2 } */
}
void int_arr_write_element_before_start_off_by_one(char x)
{
arr[-1] = x; /* { dg-warning "buffer underflow" "warning" } */
/* { dg-message "out-of-bounds write at byte -1 but 'arr' starts at byte 0" "final event" { target *-*-* } .-1 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-2 } */
}
void int_arr_write_element_at_start(char x)
@@ -33,6 +36,7 @@ void int_arr_write_element_after_end_off_by_one(char x)
arr[10] = x; /* { dg-warning "buffer overflow" "warning" } */
/* { dg-message "out-of-bounds write at byte 10 but 'arr' ends at byte 10" "final event" { target *-*-* } .-1 } */
/* { dg-message "write of 1 byte to beyond the end of 'arr'" "num bad bytes note" { target *-*-* } .-2 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-3 } */
}
void int_arr_write_element_after_end_near(char x)
@@ -40,6 +44,7 @@ void int_arr_write_element_after_end_near(char x)
arr[11] = x; /* { dg-warning "buffer overflow" "warning" } */
/* { dg-message "out-of-bounds write at byte 11 but 'arr' ends at byte 10" "final event" { target *-*-* } .-1 } */
/* { dg-message "write of 1 byte to beyond the end of 'arr'" "num bad bytes note" { target *-*-* } .-2 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-3 } */
}
void int_arr_write_element_after_end_far(char x)
@@ -47,4 +52,5 @@ void int_arr_write_element_after_end_far(char x)
arr[100] = x; /* { dg-warning "buffer overflow" "warning" } */
/* { dg-message "out-of-bounds write at byte 100 but 'arr' ends at byte 10" "final event" { target *-*-* } .-1 } */
/* { dg-message "write of 1 byte to beyond the end of 'arr'" "num bad bytes note" { target *-*-* } .-2 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-3 } */
}
@@ -6,18 +6,21 @@ void int_arr_write_element_before_start_far(int32_t x)
{
arr[-100] = x; /* { dg-warning "buffer underflow" "warning" } */
/* { dg-message "out-of-bounds write from byte -400 till byte -397 but 'arr' starts at byte 0" "final event" { target *-*-* } .-1 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-2 } */
}
void int_arr_write_element_before_start_near(int32_t x)
{
arr[-2] = x; /* { dg-warning "buffer underflow" "warning" } */
/* { dg-message "out-of-bounds write from byte -8 till byte -5 but 'arr' starts at byte 0" "final event" { target *-*-* } .-1 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-2 } */
}
void int_arr_write_element_before_start_off_by_one(int32_t x)
{
arr[-1] = x; /* { dg-warning "buffer underflow" "warning" } */
/* { dg-message "out-of-bounds write from byte -4 till byte -1 but 'arr' starts at byte 0" "final event" { target *-*-* } .-1 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-2 } */
}
void int_arr_write_element_at_start(int32_t x)
@@ -35,6 +38,7 @@ void int_arr_write_element_after_end_off_by_one(int32_t x)
arr[10] = x; /* { dg-warning "buffer overflow" "warning" } */
/* { dg-message "out-of-bounds write from byte 40 till byte 43 but 'arr' ends at byte 40" "final event" { target *-*-* } .-1 } */
/* { dg-message "write of 4 bytes to beyond the end of 'arr'" "num bad bytes note" { target *-*-* } .-2 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-3 } */
}
void int_arr_write_element_after_end_near(int32_t x)
@@ -42,6 +46,7 @@ void int_arr_write_element_after_end_near(int32_t x)
arr[11] = x; /* { dg-warning "buffer overflow" "warning" } */
/* { dg-message "out-of-bounds write from byte 44 till byte 47 but 'arr' ends at byte 40" "final event" { target *-*-* } .-1 } */
/* { dg-message "write of 4 bytes to beyond the end of 'arr'" "num bad bytes note" { target *-*-* } .-2 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-3 } */
}
void int_arr_write_element_after_end_far(int32_t x)
@@ -49,4 +54,5 @@ void int_arr_write_element_after_end_far(int32_t x)
arr[100] = x; /* { dg-warning "buffer overflow" "warning" } */
/* { dg-message "out-of-bounds write from byte 400 till byte 403 but 'arr' ends at byte 40" "final event" { target *-*-* } .-1 } */
/* { dg-message "write of 4 bytes to beyond the end of 'arr'" "num bad bytes note" { target *-*-* } .-2 } */
+ /* { dg-message "valid subscripts for 'arr' are '\\\[0\\\]' to '\\\[9\\\]'" "valid subscript note" { target *-*-* } .-3 } */
}