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File 1145-arm-jit-Use-erlang-style-labels-in-asm-dump.patch of Package erlang (Revision 63a1bfb33d7f4fc528be33fc9d548213)

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From 0f0fdfc0d7322680746200194183ddc8043d4bf1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Mon, 21 Jun 2021 08:11:14 +0200
Subject: [PATCH 5/7] arm-jit: Use erlang-style labels in asm dump

When running with `+JDdump true` the most verbose arm-assembly dump is
produced by the debug emulator. In it, labels present in the
beam-assembly are printed as `label_<index>`. This patch improves the
readability of the arm-assembly dumps by pretty-printing the label
marking the start of a function using the form
@Mod:Name/Arity-SequenceNumber.

Compared to the corresponding functionality on x86, this feature is
more complex to implement on Arm as with the trampolines used to
extend extend the range of branches, beam-level and Arm-assembly
labels no longer have one-to-one relationship.

Previously pretty-printing in the `label_<index>` format was only
available in the debug emulator. Readability and the ease with which a
user can cross-correlate arm-assembly and beam-assembly dumps is
significantly improved with pretty-printed labels, thus this patch
enables the functionality as soon as `+JDdump true` is enabled.
---
 erts/emulator/beam/jit/arm/beam_asm.hpp       | 15 +++-
 .../emulator/beam/jit/arm/beam_asm_module.cpp | 75 +++++++++++++++----
 2 files changed, 75 insertions(+), 15 deletions(-)

diff --git a/erts/emulator/beam/jit/arm/beam_asm.hpp b/erts/emulator/beam/jit/arm/beam_asm.hpp
index a9b11bb94d..fbd42ba962 100644
--- a/erts/emulator/beam/jit/arm/beam_asm.hpp
+++ b/erts/emulator/beam/jit/arm/beam_asm.hpp
@@ -920,6 +920,17 @@ class BeamModuleAssembler : public BeamAssembler {
     typedef std::unordered_map<BeamLabel, Label> LabelMap;
     LabelMap rawLabels;
 
+    /* Map of label number to function name. Only defined for the
+     * entry label of a function. This map will be populated and
+     * used only when assembly output has been requested. */
+    typedef std::unordered_map<BeamLabel, std::string> LabelNames;
+    LabelNames labelNames;
+
+    /* Sequence number used to create unique named labels by
+     * resolve_label(). Only used when assembly output has been
+     * requested. */
+    long labelSeq = 0;
+
     struct patch {
         Label where;
         uint64_t val_offs;
@@ -1213,7 +1224,9 @@ protected:
      * When the branch type is not `dispUnknown`, this must be used
      * _IMMEDIATELY BEFORE_ the instruction that the label is used in. */
     Label resolve_beam_label(const ArgVal &Label, enum Displacement disp);
-    Label resolve_label(Label target, enum Displacement disp);
+    Label resolve_label(Label target,
+                        enum Displacement disp,
+                        std::string *name = nullptr);
 
     /* Resolves a shared fragment, creating a trampoline that loads the
      * appropriate address before jumping there.
diff --git a/erts/emulator/beam/jit/arm/beam_asm_module.cpp b/erts/emulator/beam/jit/arm/beam_asm_module.cpp
index c0728c8f34..17a1385fca 100644
--- a/erts/emulator/beam/jit/arm/beam_asm_module.cpp
+++ b/erts/emulator/beam/jit/arm/beam_asm_module.cpp
@@ -19,6 +19,7 @@
  */
 
 #include <algorithm>
+#include <sstream>
 #include <float.h>
 
 #include "beam_asm.hpp"
@@ -88,18 +89,44 @@ BeamModuleAssembler::BeamModuleAssembler(BeamGlobalAssembler *ga,
     _veneers.reserve(num_labels + 1);
     rawLabels.reserve(num_labels + 1);
 
-    for (unsigned i = 1; i < num_labels; i++) {
-        Label lbl;
-
-#ifdef DEBUG
-        std::string lblName = "label_" + std::to_string(i);
-        lbl = a.newNamedLabel(lblName.data());
-#else
-        lbl = a.newLabel();
-#endif
-
-        rawLabels[i] = lbl;
+    if (erts_jit_asm_dump && named_labels) {
+        BeamFile_ExportEntry *e = &named_labels->entries[0];
+        for (unsigned i = 1; i < num_labels; i++) {
+            Label lbl;
+            char tmp[512]; // Large enough to hold most realistic
+                           // function names. We will truncate too
+                           // long names, but as the label name is not
+                           // important for the functioning of asmjit
+                           // and this functionality is probably only
+                           // used by developers, we don't bother with
+                           // dynamic allocation.
+            // The named_labels are sorted, so no need for a search.
+            if ((unsigned)e->label == i) {
+                erts_snprintf(tmp, sizeof(tmp), "%T/%d", e->function, e->arity);
+                lbl = a.newNamedLabel(tmp);
+                labelNames[i] = tmp;
+                e++;
+            } else {
+                std::string lblName = "label_" + std::to_string(i);
+                lbl = a.newNamedLabel(lblName.data());
+            }
+            rawLabels[i] = lbl;
+        }
+        return;
     }
+    if (erts_jit_asm_dump) {
+        // There is no naming info, but dumping of the assembly code
+        // has been requested, so do the best we can and number the
+        // labels.
+        for (unsigned i = 1; i < num_labels; i++) {
+            std::string lblName = "label_" + std::to_string(i);
+            rawLabels[i] = a.newNamedLabel(lblName.data());
+        }
+        return;
+    }
+    // No output is requested, go with unnamed labels
+    for (unsigned i = 1; i < num_labels; i++)
+        rawLabels[i] = a.newLabel();
 }
 
 BeamModuleAssembler::BeamModuleAssembler(BeamGlobalAssembler *ga,
@@ -549,10 +576,17 @@ void BeamModuleAssembler::patchStrings(char *rw_base,
 Label BeamModuleAssembler::resolve_beam_label(const ArgVal &Lbl,
                                               enum Displacement disp) {
     ASSERT(Lbl.isLabel());
-    return resolve_label(rawLabels[Lbl.getValue()], disp);
+    auto it = labelNames.find(Lbl.getValue());
+    if (it != labelNames.end()) {
+        return resolve_label(rawLabels[Lbl.getValue()], disp, &it->second);
+    } else {
+        return resolve_label(rawLabels[Lbl.getValue()], disp);
+    }
 }
 
-Label BeamModuleAssembler::resolve_label(Label target, enum Displacement disp) {
+Label BeamModuleAssembler::resolve_label(Label target,
+                                         enum Displacement disp,
+                                         std::string *labelName) {
     ssize_t currOffset = a.offset();
 
     ssize_t minOffset = currOffset - disp;
@@ -587,9 +621,22 @@ Label BeamModuleAssembler::resolve_label(Label target, enum Displacement disp) {
         }
     }
 
+    Label anchor;
+    if (!labelName) {
+        anchor = a.newLabel();
+    } else {
+        /* This is the entry label for a function. Create an unique
+         * name for the anchor label. It is necessary to include a
+         * sequence number in the label name because if the module is
+         * huge more than one veneer can be created for each entry
+         * label. */
+        std::stringstream name;
+        name << '@' << *labelName << '-' << labelSeq++;
+        anchor = a.newNamedLabel(name.str().c_str());
+    }
     auto it = _veneers.emplace(target.id(),
                                Veneer{.latestOffset = maxOffset,
-                                      .anchor = a.newLabel(),
+                                      .anchor = anchor,
                                       .target = target});
 
     const Veneer &veneer = it->second;
-- 
2.26.2

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File 1145-arm-jit-Use-erlang-style-labels-in-asm-dump.patch of Package erlang (Revision 63a1bfb33d7f4fc528be33fc9d548213)

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