forked from Imagelibrary/binutils-gdb
bb9d5f81c3
PR 12526 reports that -location watchpoints against bitfield arguments trigger false positives when bits around the bitfield, but not the bitfield itself, are modified. This happens because -location watchpoints naturally operate at the byte level, not at the bit level. When the address of a bitfield lvalue is taken, information about the bitfield (i.e. its offset and size) is lost in the process. This information must first be retained throughout the lifetime of the -location watchpoint. This patch achieves this by adding two new fields to the watchpoint struct: val_bitpos and val_bitsize. These fields are set when a watchpoint is first defined in watch_command_1. They are both equal to zero if the watchpoint is not a -location watchpoint or if the argument is not a bitfield. Then these bitfield parameters are used inside update_watchpoint and watchpoint_check to extract the actual value of the bitfield from the watchpoint address, with the help of a local helper function extract_bitfield_from_watchpoint_value. Finally when creating a HW breakpoint pointing to a bitfield, we optimize the address and length of the breakpoint. By skipping over the bytes that don't cover the bitfield, this step reduces the frequency at which a read watchpoint for the bitfield is triggered. It also reduces the number of times a false-positive call to check_watchpoint is triggered for a write watchpoint. gdb/ PR breakpoints/12526 * breakpoint.h (struct watchpoint): New fields val_bitpos and val_bitsize. * breakpoint.c (watch_command_1): Use these fields to retain bitfield information. (extract_bitfield_from_watchpoint_value): New function. (watchpoint_check): Use it. (update_watchpoint): Use it. Optimize the address and length of a HW watchpoint pointing to a bitfield. * value.h (unpack_value_bitfield): New prototype. * value.c (unpack_value_bitfield): Make extern. gdb/testsuite/ PR breakpoints/12526 * gdb.base/watch-bitfields.exp: New file. * gdb.base/watch-bitfields.c: New file.
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