[sancov] pc_guard_init is called once per DSO.

[aizatsky]

Summary

Documentation update for https://reviews.llvm.org/D29662

[aizatsky]

I think that keeping more general "may be called multiple times" is still correct and does give us room to maneuver.

[aizatsky]

reworded to say may be called more than once.

[aizatsky]

added at least.

[kcc]

LGTM

docs/SanitizerCoverage.rst

 
 Every edge will have its own `guard_variable` (uint32_t).
 
 The compler will also insert a module constructor that will call
 
 .. code-block:: c++
 
    // The guards are [start, stop).
-   // This function may be called multiple times with the same values of start/stop.
+   // This function will be called once with the same values of start/stop
+   // (once per DSO).
    __sanitizer_cov_trace_pc_guard_init(uint32_t *start, uint32_t *stop);
 
 With `trace-pc-guards,indirect-calls`
 ``__sanitizer_cov_trace_pc_indirect(void *callee)`` will be inserted on every indirect call.
 
 The functions `__sanitizer_cov_trace_pc_*` should be defined by the user.
 
 Example: 
 
 .. code-block:: c++
 
   // trace-pc-guard-cb.cc
   #include <stdint.h>
   #include <stdio.h>
   #include <sanitizer/coverage_interface.h>
 
   // This callback is inserted by the compiler as a module constructor
-  // into every compilation unit. 'start' and 'stop' correspond to the
+  // into every DSO. 'start' and 'stop' correspond to the
   // beginning and end of the section with the guards for the entire
-  // binary (executable or DSO) and so it will be called multiple times
-  // with the same parameters.
+  // binary (executable or DSO) and so it can be called multiple times
+  // but not with the same parameters.
   extern "C" void __sanitizer_cov_trace_pc_guard_init(uint32_t *start,
                                                       uint32_t *stop) {
     static uint64_t N;  // Counter for the guards.
     if (start == stop || *start) return;  // Initialize only once.
     printf("INIT: %p %p\n", start, stop);
     for (uint32_t *x = start; x < stop; x++)
       *x = ++N;  // Guards should start from 1.
   }