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author | Joel Brobecker <brobecker@adacore.com> | 2014-09-19 18:00:07 -0400 |
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committer | Joel Brobecker <brobecker@adacore.com> | 2014-11-17 07:23:27 +0400 |
commit | 43968415b0025fa8e1fa5c813e53e87ae392e977 (patch) | |
tree | 1be4b9f060e01c45551a91b758611e1644431024 /gdb | |
parent | abdef8eb901ce829fdc9fbe7eb89c8327c262f07 (diff) | |
download | gdb-43968415b0025fa8e1fa5c813e53e87ae392e977.zip gdb-43968415b0025fa8e1fa5c813e53e87ae392e977.tar.gz gdb-43968415b0025fa8e1fa5c813e53e87ae392e977.tar.bz2 |
[gdbserver/lynx] spurious failure to write in inferior memory
We noticed the following error on ppc-lynx178, using just about
any program:
(gdb) tar remote mytarget:4444
Remote debugging using mytarget:4444
0x000100c8 in _start ()
(gdb) b try
Breakpoint 1 at 0x10844: file try.adb, line 11.
(gdb) cont
Continuing.
!!!-> Cannot remove breakpoints because program is no longer writable.
!!!-> Further execution is probably impossible.
Breakpoint 1, try () at try.adb:11
11 Local : Integer := 18;
And, of course, trying to continue yielded the expected outcome:
(gdb) c
Continuing.
warning: Error removing breakpoint 1
Cannot remove breakpoints because program is no longer writable.
Further execution is probably impossible.
It turns out that the problem is caused by an intentional test
against a variable with an undefined value. After GDB receives
notification of the inferior stopping, it tries to remove the
breakpoint by sending a memory-write packet ("X10844,4:9 ").
This leads us to lynx_write_memory, where it tries to split
the memory-write into chunks of 4 bytes. And, in order to handle
writes which are not aligned on word boundaries, we have the
following code:
if (skip > 0 || truncate > 0)
/* We need to read the memory at this address in order to preserve
the data that we are not overwriting. */
lynx_read_memory (addr, (unsigned char *) &buf, xfer_size);
if (errno)
return errno;
(the comment explains what the code is about).
Unfortunately, the not-so-glaring error that we've made here is
that we're checking ERRNO regardless of whether we've called
lynx_read_memory. In our case, because we are writing 4 bytes
aligned on a word boundary, we do not call lynx_read_memory and
therefore test an ERRNO with an undefined value.
gdb/gdbserver/ChangeLog:
* lynx-low.c (lynx_write_memory): Put lynx_read_memory and
corresponding ERRNO check in same block.
Diffstat (limited to 'gdb')
-rw-r--r-- | gdb/gdbserver/ChangeLog | 5 | ||||
-rw-r--r-- | gdb/gdbserver/lynx-low.c | 12 |
2 files changed, 12 insertions, 5 deletions
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index 5a42642..0c25069 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,3 +1,8 @@ +2014-11-17 Joel Brobecker <brobecker@adacore.com> + + * lynx-low.c (lynx_write_memory): Put lynx_read_memory and + corresponding ERRNO check in same block. + 2014-11-12 Pedro Alves <palves@redhat.com> * server.c (cont_thread): Update comment. diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c index 96dea03..6178e03 100644 --- a/gdb/gdbserver/lynx-low.c +++ b/gdb/gdbserver/lynx-low.c @@ -688,11 +688,13 @@ lynx_write_memory (CORE_ADDR memaddr, const unsigned char *myaddr, int len) if (addr + xfer_size > memaddr + len) truncate = addr + xfer_size - memaddr - len; if (skip > 0 || truncate > 0) - /* We need to read the memory at this address in order to preserve - the data that we are not overwriting. */ - lynx_read_memory (addr, (unsigned char *) &buf, xfer_size); - if (errno) - return errno; + { + /* We need to read the memory at this address in order to preserve + the data that we are not overwriting. */ + lynx_read_memory (addr, (unsigned char *) &buf, xfer_size); + if (errno) + return errno; + } memcpy ((gdb_byte *) &buf + skip, myaddr + (addr - memaddr) + skip, xfer_size - skip - truncate); errno = 0; |