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Teach DTrace about BTI on arm64
The Branch Target Identification (BTI) Armv8-A extension adds new instructions that can be placed where we may indirrectly branch to, e.g. at the start of a function called via a function pointer. We can't emulate these in DTrace as the kernel will have raised a different exception before the DTrace handler has run. Skip over the BTI instruction if it's used as the first instruction in a function. Sponsored by: The FreeBSD Foundation
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@ -2466,6 +2466,9 @@ extern void dtrace_helpers_destroy(proc_t *);
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#define B_DATA_MASK 0x00ffffff
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#define B_INSTR 0x14000000
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#define BTI_MASK 0xffffff3f
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#define BTI_INSTR 0xd503241f
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#define NOP_INSTR 0xd503201f
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#define RET_INSTR 0xd65f03c0
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@ -118,6 +118,14 @@ fbt_provide_module_function(linker_file_t lf, int symindx,
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instr = (uint32_t *)(symval->value);
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limit = (uint32_t *)(symval->value + symval->size);
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/*
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* Ignore any bti instruction at the start of the function
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* we need to keep it there for any indirect branches calling
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* the function on Armv8.5+
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*/
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if ((*instr & BTI_MASK) == BTI_INSTR)
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instr++;
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/* Look for stp (pre-indexed) operation */
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found = false;
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/*
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