<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Thanks, got it!<div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Feb 25, 2019, at 12:26 PM, Ben Craig <<a href="mailto:ben.craig@ni.com" class="">ben.craig@ni.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(255, 255, 255); color: rgb(255, 255, 255); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none;"><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Existence of unwind information is a runtime property. It is possible for a given binary to have zero unwind information. The easiest example is a 32-bit x86 Windows binary (and maybe Linux?) built with frame-pointer-omission. There are no unwind tables in that situation, and you can’t just follow frame pointers backwards, because they don’t exist. This kind of unwinding generally requires debug information. Maybe, in some specific cases, you could analyze the assembly to figure out how to unwind it, but in the general case, that requires solving the halting problem.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Embedded platforms often omit all unwinding information to save space.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">If you have a recent instruction pointer from user code, then just reporting that one instruction pointer can still be useful.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="border-style: none none none solid; border-left-width: 1.5pt; border-left-color: blue; padding: 0in 0in 0in 4pt;" class=""><div class=""><div style="border-style: solid none none; border-top-width: 1pt; border-top-color: rgb(225, 225, 225); padding: 3pt 0in 0in;" class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><b class="">From:</b><span class="Apple-converted-space"> </span>llvm-dev <<a href="mailto:llvm-dev-bounces@lists.llvm.org" class="">llvm-dev-bounces@lists.llvm.org</a>><span class="Apple-converted-space"> </span><b class="">On Behalf Of<span class="Apple-converted-space"> </span></b>Julian Lettner via llvm-dev<br class=""><b class="">Sent:</b><span class="Apple-converted-space"> </span>Monday, February 25, 2019 1:30 PM<br class=""><b class="">To:</b><span class="Apple-converted-space"> </span><a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a><br class=""><b class="">Subject:</b><span class="Apple-converted-space"> </span>[EXTERNAL] [llvm-dev] [Sanitizers] Platforms that don't support stack unwinding<o:p class=""></o:p></div></div></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Hi,<o:p class=""></o:p></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">In sanitizer code we have two notions of stack unwinders: fast and slow. [1] In the context of sanitizers, stack unwinding is most often for printing error reports that include a stack trace.<o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I am currently trying to fix an issue that is related to some platforms (Darwin) only supporting the fast unwinder, but calling code not being aware of that possibility.<o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">My mental model was that platforms are required to at least support one kind of unwinder, so I turned a runtime check [2] into a compile time assert [3]. Apparently this is not the case.<o:p class=""></o:p></div></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">What do (or should) we do on platforms without supported unwinders? <o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Or is my mental model correct, and this a runtime (instead of compile time) check for other reasons? Compilation/build system convenience?<o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Thanks,<o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Julian<o:p class=""></o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">[1] <a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_llvm_llvm-2Dproject_blob_fcbd7f64953b04f42dd59f606e45dc8e88a27548_compiler-2Drt_lib_sanitizer-5Fcommon_sanitizer-5Fstacktrace.h-23L21&d=DwMFAg&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=y8mub81SfUi-UCZRX0Vl1g&m=PyWoz5dhVQq4Qd3o66DlXu836tgSHFc2XCX0gHQyHoM&s=xPhup1hvHzIkL7yBEi03pLgh3ntvnZwqBzo-n-KzrMc&e=" style="color: purple; text-decoration: underline;" class="">https://github.com/llvm/llvm-project/blob/fcbd7f64953b04f42dd59f606e45dc8e88a27548/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h#L21</a><o:p class=""></o:p></div></div><div class=""><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">[2]<span class="Apple-converted-space"> </span><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_llvm_llvm-2Dproject_blob_fcbd7f64953b04f42dd59f606e45dc8e88a27548_compiler-2Drt_lib_sanitizer-5Fcommon_sanitizer-5Fstacktrace-5Flibcdep.cc-23L78&d=DwMFAg&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=y8mub81SfUi-UCZRX0Vl1g&m=PyWoz5dhVQq4Qd3o66DlXu836tgSHFc2XCX0gHQyHoM&s=Y3jCglxBAPEjTrHwT0YsdIFdEsfw8LLkKWs4YUxxH70&e=" style="color: purple; text-decoration: underline;" class="">https://github.com/llvm/llvm-project/blob/fcbd7f64953b04f42dd59f606e45dc8e88a27548/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_libcdep.cc#L78</a><o:p class=""></o:p></div></div></div><div class=""><div class=""><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">[3]<span class="Apple-converted-space"> </span><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_llvm_llvm-2Dproject_blob_fcbd7f64953b04f42dd59f606e45dc8e88a27548_compiler-2Drt_lib_sanitizer-5Fcommon_sanitizer-5Fstacktrace.h-23L21&d=DwMFAg&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=y8mub81SfUi-UCZRX0Vl1g&m=PyWoz5dhVQq4Qd3o66DlXu836tgSHFc2XCX0gHQyHoM&s=xPhup1hvHzIkL7yBEi03pLgh3ntvnZwqBzo-n-KzrMc&e=" style="color: purple; text-decoration: underline;" class="">https://github.com/llvm/llvm-project/blob/fcbd7f64953b04f42dd59f606e45dc8e88a27548/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h#L21</a></div></div></div></div></div></div></blockquote></div><br class=""></div></div></div></div></div></div></div></div></div></div></div></body></html>