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| <h4 class="subsection">5.1.10 “Breakpoint address adjusted...”</h4> |
| |
| <p><a name="index-breakpoint-address-adjusted-283"></a> |
| Some processor architectures place constraints on the addresses at |
| which breakpoints may be placed. For architectures thus constrained, |
| <span class="sc">gdb</span> will attempt to adjust the breakpoint's address to comply |
| with the constraints dictated by the architecture. |
| |
| <p>One example of such an architecture is the Fujitsu FR-V. The FR-V is |
| a VLIW architecture in which a number of RISC-like instructions may be |
| bundled together for parallel execution. The FR-V architecture |
| constrains the location of a breakpoint instruction within such a |
| bundle to the instruction with the lowest address. <span class="sc">gdb</span> |
| honors this constraint by adjusting a breakpoint's address to the |
| first in the bundle. |
| |
| <p>It is not uncommon for optimized code to have bundles which contain |
| instructions from different source statements, thus it may happen that |
| a breakpoint's address will be adjusted from one source statement to |
| another. Since this adjustment may significantly alter <span class="sc">gdb</span>'s |
| breakpoint related behavior from what the user expects, a warning is |
| printed when the breakpoint is first set and also when the breakpoint |
| is hit. |
| |
| <p>A warning like the one below is printed when setting a breakpoint |
| that's been subject to address adjustment: |
| |
| <pre class="smallexample"> warning: Breakpoint address adjusted from 0x00010414 to 0x00010410. |
| </pre> |
| <p>Such warnings are printed both for user settable and <span class="sc">gdb</span>'s |
| internal breakpoints. If you see one of these warnings, you should |
| verify that a breakpoint set at the adjusted address will have the |
| desired affect. If not, the breakpoint in question may be removed and |
| other breakpoints may be set which will have the desired behavior. |
| E.g., it may be sufficient to place the breakpoint at a later |
| instruction. A conditional breakpoint may also be useful in some |
| cases to prevent the breakpoint from triggering too often. |
| |
| <p><span class="sc">gdb</span> will also issue a warning when stopping at one of these |
| adjusted breakpoints: |
| |
| <pre class="smallexample"> warning: Breakpoint 1 address previously adjusted from 0x00010414 |
| to 0x00010410. |
| </pre> |
| <p>When this warning is encountered, it may be too late to take remedial |
| action except in cases where the breakpoint is hit earlier or more |
| frequently than expected. |
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