Add Linux GCC floor test to Abseil GitHub Actions CI.

Configures the remote-floor RBE platform and adds the Linux GCC/libstdc++ (floor) job to the GitHub Actions CI matrix using the oss-linux-floor and oss-linux-toolchain-floor Docker images. Also passes suffix.size() explicitly to substr() in absl::EndsWith to avoid a false-positive -Werror=stringop-overread warning under GCC 11 at -O2.

PiperOrigin-RevId: 1001113554

.bazelrc

diff --git a/.bazelrc b/.bazelrc
index b1c92dd..c39ac4e 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -77,6 +77,11 @@
 build:remote --remote_executor=grpcs://us-east1-remotebuildexecution.googleapis.com
 build:remote --remote_instance_name=projects/google.com:absl-177019/instances/absl-ci-east
 
+build:remote-floor --config=remote
+build:remote-floor --extra_execution_platforms=//ci:rbe-floor
+build:remote-floor --host_platform=//ci:rbe-floor
+build:remote-floor --platforms=//ci:rbe-floor
+
 build:remote-arm --config=remote-base
 build:remote-arm --extra_execution_platforms=//ci:rbe-arm
 build:remote-arm --host_platform=//ci:rbe-arm

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 15f6c95..a761a51 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -44,9 +44,8 @@
   cancel-in-progress: ${{ contains(fromJSON('["pull_request", "workflow_dispatch", "schedule"]'), github.event_name) }}
 
 jobs:
-  # Mirrors the 10 Linux "latest" Bazel Kokoro jobs (parallelized to 1 job per
-  # Bazel invocation). Not yet covered here:
-  #   - "Linux GCC/libstdc++ (floor) Bazel" (requires a floor GCC Docker image)
+  # Mirrors the 11 Linux Bazel Kokoro jobs (parallelized to 1 job per Bazel
+  # invocation). Not yet covered here:
   #   - CMake, macOS, and Windows Kokoro jobs
   linux:
     name: Linux ${{ matrix.config.name }} Bazel
@@ -87,18 +86,25 @@
           - name: GCC/libstdc++ alternate options
             toolchain: gcc
             alternate_options: true
+          # linux_gcc-floor_libstdcxx_bazel.cfg (c++17 only)
+          - name: GCC/libstdc++ (floor)
+            toolchain: gcc
+            remote_config: remote-floor
+            container_image: gcr.io/google.com/absl-177019/oss-linux-toolchain-floor@sha256:f3d8a0f76a88d5edbba70250de47fb862271297b9ff41ff317240e564c95d65e
+            stds: '["c++17"]'
           # linux_arm_clang-latest_libcxx_bazel.cfg (c++17 and c++20 only)
           - name: ARM64 Clang/libc++
+            os: ubuntu-24.04-arm
             toolchain: clang-arm
-            arch_suffix: -arm
+            remote_config: remote-arm
             stds: '["c++17", "c++20"]'
     uses: ./.github/workflows/bazel.yml
     secrets: inherit
     with:
-      os: ubuntu-24.04${{ matrix.config.arch_suffix }}
+      os: ${{ matrix.config.os || 'ubuntu-24.04' }}
       toolchain: ${{ matrix.config.toolchain }}
-      remote_config: remote${{ matrix.config.arch_suffix }}
-      container_image: gcr.io/google.com/absl-177019/oss-linux-toolchain-latest@sha256:8dfd8bff496cce2b3aaa5d2f1b63ebb6790f2bc78a02cdc0ca9898372fbc38f3
+      remote_config: ${{ matrix.config.remote_config || 'remote' }}
+      container_image: ${{ matrix.config.container_image || 'gcr.io/google.com/absl-177019/oss-linux-toolchain-latest@sha256:8dfd8bff496cce2b3aaa5d2f1b63ebb6790f2bc78a02cdc0ca9898372fbc38f3' }}
       alternate_options: ${{ matrix.config.alternate_options || false }}
       stds: ${{ matrix.config.stds || '["c++17", "c++20", "c++23"]' }}
       compilation_modes: ${{ matrix.config.compilation_modes || '["opt", "fastbuild"]' }}

absl/strings/match.h

diff --git a/absl/strings/match.h b/absl/strings/match.h
index 431d4f5..65bd8aa 100644
--- a/absl/strings/match.h
+++ b/absl/strings/match.h
@@ -80,7 +80,8 @@
   if (text.size() < suffix.size()) {
     return false;
   }
-  absl::string_view possible_match = text.substr(text.size() - suffix.size());
+  absl::string_view possible_match =
+      text.substr(text.size() - suffix.size(), suffix.size());
   return possible_match == suffix;
 }
 // StrContainsIgnoreCase()

ci/BUILD.bazel

diff --git a/ci/BUILD.bazel b/ci/BUILD.bazel
index f8a7e58..d0e2b8f 100644
--- a/ci/BUILD.bazel
+++ b/ci/BUILD.bazel
@@ -29,6 +29,20 @@
 )
 
 platform(
+    name = "rbe-floor",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:x86_64",
+    ],
+    exec_properties = {
+        "OSArch": "amd64",
+        "cache-silo-key": "n2-highcpu-2-2026-10-14",
+        "container-image": "docker://gcr.io/google.com/absl-177019/oss-linux-floor@sha256:81041c514c7ee412a5677afc652b9eb3a02e0f6dfe8d71164d80e6e39820b09d",
+        "dockerRunAsRoot": "true",
+    },
+)
+
+platform(
     name = "rbe-arm",
     constraint_values = [
         "@platforms//os:linux",